Here's something I did a while back (as my first big skin pack, no less), but never actually uploaded (since it was only really due to personal/clan preference). It's fairly straightforward, and changes the default Czechoslovak tanks' color from brown to primer grey (a little lighter and flatter than German dunkelgrau). This probably isn't a historical color at all; I only did it because I didn't really like the original brown. Didn't really think I'd upload this, but I ran out of space on my computer for it, and Dropbox/Google Drive didn't exactly have space for it either, so I just stuck it on the download hub, and... the rest is history?
To find out how to get the in-game customization system to work properly with this pack, head over to the Customization Install Guide page and follow the instructions listed there. If you're looking for this pack's color code, here it is: