PDFs cannot be colored in InDesign (or any other graphic application I'm familiar with). You either make small edits in Acrobat, or you recreate the original artwork.
I appreciate it Steve! Yes, there is a television program, or use to be!
The one we had way back when, was a Chyron unit; and you could take a gray
scale drawing of a person from any source, including shooting a picture
with the studio camera, then color each item of clothing, on the person,
Depending upon the PDF, you can open it for editing in AI or a dozen other applications. This will range from creating more work for you (recreating flattened effects, etc) to it simply opens great. A lot depends upon the originating application.
But, can you not get the original source? That is 100% the very best thing you could get.