Changing the Alpha Slider on Color Picker changes RGB values on some colors

[noknokcody]

Description

When using some RGBA colors on the color picker, adjusting the alpha slider also adjusts RGB values slightly. For example, if you enter the RGBA values 246, 110, 4, 1 on an Alpha-Enabled color picker and then adjust the Alpha slider, the Green value of "110" get's changed to "109". While the color change is minimal to the human eye, it makes it impossible to detect whether a change to the RGB values was intentional or not which is what I'm trying to detect.

Step-by-step reproduction instructions

1. Go to https://wordpress.github.io/gutenberg/?path=/docs/components-colorpicker--alpha-enabled
2. Change the RGBA values to 246, 110, 4, 1 (You may need to click outside the box to trigger an state update)
3. Adjust the Alpha slider to any value

Expected behaviour

When adjusting the Alpha slider using this preset color configuration the none of the RGB values should change. Only the Alpha value

Actual behaviour

The green value changes from 110 to 109

Screenshots or screen recording (optional)

WordPress information

No Wordpress (Using github.io)

Device information

• Device: Desktop Computer
• Operating system: Windows 10
• Browser: Chrome 88.0.4324.104 (Official Build) (64-bit)

[talldan]

Thanks for reporting this. It seems like it always changes by 1, which makes me wonder if it's a rounding issue.

[noknokcody]

I thought something similar although I believe I found a few colors where the number was changing by more than 1 value. Not sure if that helps or not. Will report back if I find any more info :)

[mirka]

Looks like an upstream bug in react-colorful (omgovich/react-colorful#163). I can reproduce it in this sandbox.

[t-hamano]

I am not sure if this is an appropriate fix, but I wrote a PR for the library.
Hopefully this PR works correctly 😅