Make "Pick Color"'s result less precise, keep only 3 decimals

[jsjtxietian]

This fixes half of #89354 , the other half I did not observe the problem yet.

The number of decimals is arbitrary, but I suppose 2-3 should be enough.

[MewPurPur]

Title of the issue could also be renamed as now it's 3 places.

[ajreckof]

I'm wondering if this should not use the value inside the Hex value it already truncate to 3 decimals and moreover this would enable switching between hex and float values.

[Calinou]

Tested locally (rebased on top of master 2149682), it works as expected.

Rounding to 3 decimals is sufficient to represent any 32-bit color (e.g. in the form of #rrggbbaa), so it's fine.

[akien-mga]

Thanks!