Screen brightness, night mode and colouring
The same picture is harder to colour at night, and the reason is on your device rather than in your eyes. Warm-shift modes compress the blues; low brightness compresses the darks.
You worked on a picture in the afternoon without difficulty. You pick it up at eleven at night and two of the colours look like the same colour, the dark tones have gone muddy, and you find yourself tapping regions to see what happens. Nothing about the picture has changed. Your display has, twice over, and both changes are ones you probably switched on deliberately and then forgot about.
Warm modes eat the blue end
Night Shift, night light, comfort view, reading mode — the names differ, the mechanism is the same. The display reduces its blue output and, to a lesser extent, its green, so the whole screen shifts towards amber. On most devices this ramps up automatically after sunset, which is precisely when you are least likely to connect it to a problem that has just appeared.
For a photograph or a page of text this is harmless. For a task that requires you to tell two neighbouring colours apart, it is not, and the damage is concentrated in specific places.
- Two blues that were clearly different can collapse into each other, because you have turned down the channel that carried the difference between them.
- Cool greys drift warm, so a grey palette that was ordered from cool to neutral loses its ordering and reads as a set of near-identical beiges.
- Purples and blue-leaning greens lose their distinguishing component and move towards their neighbours.
- Warm colours are relatively unaffected, which is why a picture full of reds and oranges seems fine and one built from sea colours falls apart.
So the first thing to do when two numbered colours look identical at night is not to squint harder. It is to turn the warm mode off for ten seconds and look again. If they separate cleanly, you have your answer, and you know that the palette is fine and your eyes are fine.
Low brightness eats the dark end
The second change is brightness, and it hits the opposite end of the range. Auto-brightness in a dark room drops the display luminance a long way, which is comfortable and correct for reading. What it also does is compress the absolute differences between tones — and the compression is not even. Two dark tones that differed by a small amount at full brightness differ by an even smaller amount at low brightness, and at some point the difference falls below what you can reliably see.
There is a limit to how fine a difference in lightness anyone can detect, and it is proportional rather than absolute: the darker the pair, the larger the difference has to be before you notice it. Dimming the screen pushes your dark tones into exactly the region where that threshold bites. The light end survives dimming far better, which is why the shadows go first and the highlights hold.
On OLED displays there is an additional wrinkle at the very bottom of the brightness range, where the number of distinguishable steps available in the near-black tones is genuinely small. A gradient that was smooth at midday can show visible banding, and two dark palette entries can become one. This is a property of the panel at that brightness, not a fault in the artwork.
What to do about it
None of this argues for colouring under a floodlight. It argues for knowing which of two knobs to turn, and when.
- When two colours look the same, toggle the warm mode off before anything else. It takes a second from the control centre and it is diagnostic: if the problem vanishes, you have found it.
- For a picture with a lot of dark or cool tones, either work on it earlier or turn the warm mode off for the session. Some systems let you exclude nothing and it is all or nothing, so a manual toggle is the practical tool.
- Nudge the brightness up for a dark passage specifically, then put it back. You do not need a bright screen all evening — you need it for the ten minutes where you are separating four near-blacks.
- Add a small lamp rather than raising the screen. A bright screen against a dark room is the least comfortable combination there is; a dim screen in a dimly lit room is better than either extreme, and it lets you keep enough brightness to separate the darks.
- Choose lighter or higher-contrast artwork for late sessions and save the moody ones for daylight. This is not a compromise so much as a sensible pairing.
About the claims made for warm modes
It would be easy to end here with a line about protecting your eyes, and it would not be honest. The claims commonly made for warm display modes — that they protect the eyes, or meaningfully improve sleep — are weakly supported and actively contested. The studies are mostly small, short, and rely on self-reported comfort or sleep quality; some find effects, some find nothing, and the effect of the display shift is entangled with simply having a dimmer screen and with what you happen to be doing on it.
That does not make warm modes useless. A dimmer, warmer screen at night is more comfortable to look at, and comfort is a perfectly good reason to use something. Treat it as a comfort setting you can switch off freely when it gets in the way, not as a health measure you would be foolish to disable for ten minutes to check a palette.
And the usual caveat, which is not boilerplate: if colours have become hard to separate in daylight too, or if your vision has changed recently in any way you notice, that is an optometrist question. A display setting explains a difference between afternoon and midnight. It does not explain a change that persists across both.
Frequently asked questions
Why do two blues look identical in the evening but not in the day?
Almost certainly a warm display mode such as Night Shift or night light, which reduces blue output and therefore reduces the very difference that separated them. Toggling it off for a moment is both the test and the fix. Cool greys and purples suffer the same way.
Does low screen brightness make dark colours harder to tell apart?
Yes, and more than it affects light ones. The smallest difference in lightness a person can detect scales with the brightness of the pair, so dark tones need a bigger gap to be distinguishable, and dimming shrinks the gap. On OLED at very low brightness there are also fewer usable steps in the near-blacks.
Should I keep night mode on while colouring?
Keep it on if the picture is working, and switch it off when two colours refuse to separate. There is no reason to be dogmatic either way — it is a comfort setting rather than a health measure, and the claims made for warm modes protecting eyes or sleep are weakly supported and contested.
Is colouring in bed with the lights off bad for my eyes?
It is uncomfortable rather than harmful. A bright screen against a dark surround is the worst combination for comfort. Turn the brightness down and put a small lamp on somewhere behind or beside you, which fixes most of it and keeps enough brightness to separate the dark colours.
Try it on a real canvas
Numbrush is colour by number for adults: mandalas, rose windows and geometric pattern work, twelve colours a picture, a magnifier for the tight spots, and a wrong tap that costs you nothing. Free, offline, no ads and no account.