Contrast Pair Desk
Why do green and blue need different text colors in Contrast Pair Desk?
Contrast Pair Desk weights red, green and blue differently when calculating relative luminance. Full green (#00FF00) and full blue (#0000FF) therefore produce very different ratios: black text meets all four displayed thresholds on the green but falls below all four on the blue. White text reverses those outcomes. Check each exact text/background pair rather than carrying a result across a color change.
Compare two backgrounds with the same text
Suppose you are choosing between a green and a blue solid label background. Both hex values have one channel at FF and two at 00, so it might seem reasonable to keep the same text color. Contrast Pair Desk?s calculation does not treat those channels as interchangeable.
Enter #000000 in Foreground / text and #00FF00 in Background, then choose Check contrast. The ratio is 15.304:1, and all four decisions say Meets. Keep the black foreground, replace only the background with #0000FF, and check again. The ratio becomes 2.444:1, with all four decisions Below threshold. These are two separate pair checks, not a comparison mode inside the app.
Read the luminance behind the difference
The relative-luminance readout explains the change. Full green has luminance 0.715200, while full blue has luminance 0.072200. Black is 0.000000. The app is not counting how many channels are at their maximum, adding the hex digits, or averaging the three channel values.
Its implementation splits the hex value into red, green and blue channels, divides each by 255 and applies a linearization formula. It then weights those results by 0.2126 for red, 0.7152 for green and 0.0722 for blue. In these particular examples, the active channel becomes 1 and the others become 0, so the channel?s weight is also the final luminance.
For other colors, the intermediate channel conversion matters too. Do not estimate a new pair by adding or averaging its raw RGB numbers. Enter the exact values and read the calculated luminances instead.
Follow the ratio, then try white text
The app calculates contrast as the lighter luminance plus 0.05, divided by the darker luminance plus 0.05. For black on green, that is 0.7652 divided by 0.05, giving 15.304. For black on blue, it is 0.1222 divided by 0.05, giving 2.444. The same black text has much less calculated contrast against the blue.
Now keep the blue background and change Foreground / text to #FFFFFF. After Check contrast, white on blue gives 8.592:1 and Meets in all four rows. Change the background to #00FF00 and check again: white on green gives 1.372:1 and falls below every row. In these examples, the useful text choice switches when the background changes.
This is a manual comparison. The app does not search for a replacement color or adjust your palette. Nor do these examples mean every green needs black or every blue needs white; a different shade has different channel values and needs its own check.
Apply the comparison to one actual label
For your own label, enter its exact solid background and proposed text color. Read the relevant threshold row, then change only the text color to compare an alternative against the same background. A change clears the old result, so choose Check contrast for each candidate before recording its outcome.
Keep the actual typography in view. The app defines large text as at least 18 pt regular or 14 pt bold; it does not inspect the size or weight of your label. Its isolated sample is illustrative. A result for an opaque solid background does not evaluate a gradient, a photograph or transparency behind the text.
Keep the pairs separate when recording your choice
If you need both alternatives for a decision, copy or download the first report before editing the pair. Each report includes the foreground, background, their luminances, the ratio and four decisions. After checking the alternative, save that report separately with a name that identifies the pair. The app holds one current result and has no saved comparison history.
Use those records to explain the specific choice: for example, white on #0000FF meets all four displayed thresholds while black on that same background meets none. That is evidence about those two opaque pairs. Contrast alone does not establish readability or accessibility conformance for the finished label or page.
AI-assisted ForgeHub editorial. App capabilities were checked against its implementation; this guide is not an independent review.
Frequently asked questions
Does FF mean green and blue have equal luminance?
No. FF is the maximum value of that individual channel. The app linearizes each channel and gives green a weight of 0.7152 and blue a weight of 0.0722. Full green and full blue consequently have different calculated luminances.
Will making black text bold fix the full-blue example?
In the app?s threshold calculation, black on #0000FF remains 2.444:1. That is below even the 3:1 AA large-text threshold. Changing size or weight does not change the ratio of the two entered colors; check a different pair.
Can Contrast Pair Desk choose a better brand color for me?
No. It calculates one pair at a time and supports manual adjustments. It has no palette search or automatic color correction. Enter a proposed alternative and choose Check contrast to evaluate it.