I'm running a new sub-panel to my basement (the main panel is in the garage). I bought a 500' spool of 6 AWG THHN. The distance to the sub-panel is about 110' so I cut the spool into 4 x 125' lengths. I was planning on using one of the THHN cables as the ground. I just wanted to confirm that it would not be an issue running an insulated wire as the ground. I don't see why it would be a problem but just wanted to double check.
And as a follow-up, I saw one place that if you are using 6 AWG or larger you must use different colored cables. The spool I purchased is all black and I color coded each cable every couple of feet with colored tape. Is that going to be a problem or is that more of a inspector-by-inspector issue?