Here is my version of Maple: Maple 18.00, X86 64 WINDOWS, Feb 10 2014, Build ID 922027
The code you wrote renders three blue circles on my software, so the problem appears to be that I am trying to use options not available on my version. The syntax does not generate errors, but it also doesn't function the way it would on a newer version. I am trying to plot a circle (and other curves) with the color changing smoothly along the circle (or curve) as the angle or other parameter smoothly changes ('b' in the code above). Perhaps that is not possible with Maple 18.
A search on MapleSoft.com yielded information about Valuesplit option, but now that I look toward the end of the relevant page, I see this option was introduced in Maple 2016.
Thank you for your answer.