How does a warm filter change colours?

A warm filter lowers the display white point, reducing the blue and slightly the green channel relative to red. This shifts every on-screen colour toward orange, which can reduce the luminance difference between text and background and therefore the contrast ratio.

How is the warm shift simulated?

The tool computes an approximate sRGB white point for the target temperature using a blackbody model, normalised so 6500K leaves colours unchanged. Each channel of your colours is multiplied by the resulting per-channel gain and clamped to the valid range.

Which contrast thresholds are used?

WCAG 1.4.3 requires 4.5:1 for normal text and 3:1 for large text, where large means at least 18.66px bold or 24px. Tick the large-text box to use the 3:1 threshold; the tool labels each result as AAA, AA, or Fail.

Is this an exact match for a real device filter?

No. Real implementations of Night Shift, f.lux, and vendor blue-light modes use their own curves, so treat this as an early-warning check. If contrast is marginal, verify on the actual device with the filter at full strength.

Does my colour data leave the browser?

No. The temperature model and all contrast maths run locally in your browser, so your palette never leaves your device and results are instant.

Colour Temperature & Night-Mode Accessibility Checker

The Colour Temperature & Night-Mode Accessibility Checker answers a question most contrast tools ignore: does your theme still pass WCAG once a user turns on a warm night-mode or blue-light filter? Warming the display shifts every colour toward orange, and that shift can quietly push marginal text below the contrast threshold.

How it works

Model the white point. For the chosen temperature the tool computes an approximate sRGB white point using a blackbody model, normalised so 6500K (the sRGB D65 reference) produces no change. Lower temperatures cut the blue channel and part of the green channel.
Apply the shift. Each channel of your foreground and background colours is multiplied by the per-channel gain from that white point and clamped to 0 to 255, producing the warmed colours a filter would render.
Compute contrast. Using the WCAG relative-luminance formula, the tool calculates the contrast ratio of the original colours and of the warmed colours, then labels each as AAA, AA, or Fail for the selected text size.

Example

Light grey text #d0d0d0 on a near-black #101418 background passes comfortably at 6500K. Warming to 2700K drops the foreground’s blue and green channels more than the dark background’s, narrowing the luminance gap — the tool shows the new ratio and flags it if it falls under 4.5:1.

Tips and notes

If a theme is borderline at neutral temperature, assume a warm filter will break it and raise the base contrast before shipping.
Large text gets the more forgiving 3:1 threshold, so headings often survive a warm shift that body text does not.
The model is an approximation of the white-point change, not a colour-managed simulation of a specific vendor filter; verify marginal cases on a real device.