How to set original color of markers in plot legend?

Question

I tried to make a plot markers manually as follows

PointLegend[ {Black} , {"a"}, 
 LegendMarkers -> {Graphics[{EdgeForm[{Black, AbsoluteThickness[2]}], 
     FaceForm[Transparent], Rectangle[]}]}] 

However, the color of resulting legend looks a bit whitened so in this case the resulting color looks grey instead of black.

Why was the color changed and how can I fix this problem?

Answer 1

If you look at the box form of your legend (using ToBoxes) you will see that the GraphicsBox representing your marker has the option

DefaultBaseStyle -> {"Graphics", {AbsolutePointSize[6]}, 
 Directive[EdgeForm[Directive[Opacity[0.3], GrayLevel[0]]], 
 PointSize[0.5], AbsoluteThickness[1.6], GrayLevel[0]]}

Note that it includes an Opacity[0.3] in the EdgeForm, as Opacity is a separate directive, setting the color to Black is insufficient to override it. So, instead, use

EdgeForm[{Black, AbsoluteThickness[2], Opacity[1]}]

instead.

Answer 2

A quick check by running ToBoxeson your example showed a couple of Opacity[0.3] in the output (not sure why this is done), causing the ligther color. This solved the problem for me:

PointLegend[{Black}, {"a"}, 
 LegendMarkers -> {Graphics[{EdgeForm[{Black, AbsoluteThickness[2], 
       Opacity[1]}], FaceForm[White], Rectangle[]}]}, 
 LegendMarkerSize -> 200]