It's bad enough when company is treat people is independent contractors when they should pay them as employees. Arguably, since you used the companies own paints and other supplies, you should not have been classified as an independent contractor in the first place. One of the key tests the IRS uses for independent-contractor status is that you do the job with your own tools.

But then too turn around and also enforce a non-compete...

That's simply uncalled for.

If you're really an independent contractor, then you certainly ought to have the right to contract out your services to whomever is willing to buy them.

That's the whole point of being an independent contractor.