I downloaded 5-6 other skins from here
. Then I pulled up the RGBA colours from here
I opened up the files with the settings and carefully compared parameters between skins until I sort of realized what was going on. I then found another Steam Skin with a purple theme and copied the relevant parts into my own file so as to only change colour and not change anything about the layout of Steam itself. Afterwards I modified a few of the colours to match my tastes, and finished by photoshopping together the images. Took me a few hours thanks to the loads of shortcuts I took by heavily referencing and using other peoples work.
Edit: If anybody is interested in a Terran Republic skin check out the Castlevania Steam Skin in the link above. The red theme is very well done. All you need to do is change the pictures on the top and bottom of the skin.