Some colours, such as #2171b2 at 255 alpha, on a normal layer at 100% opacity, above background layers (as in any normal layer or background below) of certain values, present some transparency.
Such colours are split into no more than two shades around some point between the two example background greys (light: #877576 and dark: #817072), where the blue above the lighter grey appears unchanged as expected, but the very same blue over the darker grey appears darkened, as if slightly transparent.
The degree to which this effect can be seen seems fixed- the lighter background layer grey can be replaced with pure white and the darker grey pure black, yet the resultant effect to the colour above will not change.
Most colours do not exhibit this behaviour, such as those deviating from the example blue in only hue, only saturation or only value. For example, the given blue’s saturation in HSV view is 81, and when incrementing this down, the effect entirely ceases to present at saturation 75 and below. Similar can be observed when incrementing the other mentioned color attributes up or down.
This may be related to Eyedropper alters picked colour , which persists unless the eyedropper tool is set to sample the ‘current layer’ only.
