It IS called "The Magic Paintbrush". Michael York (Logan's Run) was the voice of the King.

But a search for the video or DVD on Amazon wasn't much help...

www.amazon.com/Magic-Paintbrush-Tom-Tataranowicz/dp/B00004CJHJ/sr=8-4/qid=1159944409/ref=sr_1_4/002-6643923-5624833?ie=UTF8&s=video

...unless you're in the UK.

www.amazon.co.uk/Magic-Paintbrush-Tom-Tataranowicz/dp/B00004CJHJ