I recommend playing with a postscript repl, either ghostscript or couple of the online ones.

http://logand.com/sw/wps/index.html#sec-1

I don't know the best resource, but Thinking in Forth should get you started.

http://thinking-forth.sourceforge.net

Since the others gave you promotional material, I'll give you a write-up that discusses the good and weird sides of it:

https://news.ycombinator.com/item?id=1680149

The weird stuff makes a lot of people decide not to use it. So, they should know ahead of time. I do think there's potential for a Forth with less weird stuff or more compatible with C. There could even be one already given a benefit of Forth is it's easy to write interpreters for it. On that note, here's a tutorial series illustrating that:

http://blog.asrpo.com/forth_tutorial_part_1

I played around with Forth last year and found it very fun. Similar to Lisp it has a simple ruleset with which you can build up abstractions that almost look like a DSL. I'd say it sits somewhere between Assembly and C. It's like writing assembly but you don't have to worry about register assignment.

Was the pun on colorForth intended? Just in case it wasn't, colorForth was also created by the creator of Forth, and color has syntactic significance here.