Quick tutorial I made, not that great, not sure if it creates a effect you want, but here it is.
First open up your pic and make a new layer on top.
Now brush your covenant splatters. I used the color 3a85af
Right click the layer and hit blending options.
Use these settings.
Inner Glow:
blending: normal
Color: Darker than the original. I used 1d3b4b
Outer Glow:
Blending: Normal
Color, around the same thing as inner glow. I used 3d5461
Size: 2
Color overlay: You can change the color here again if you want. I changed mine to 4e9cbc for fun.
Make a new layer under the splatter.
Click the splatter layer and hit ctrl+E (Merge down)
Change the merged layer to overlay in the blending mode drop down.
Play around with a soft eraser brush at different opacity erasing parts you don't like and changing the darkness of things.
Result:
