# How to set original color of markers in plot legend?

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?

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]}]


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"},