Can one block with a protection from color creature?
Declaring a creature as a blocker isn't targeting; the rules don't mention the word 'target'.


  509.1a The defending player chooses which creatures they control, if any, will block. The chosen creatures must be untapped. For each of the chosen creatures, the defending player chooses one creature for it to block that’s attacking that player or a planeswalker they control.


If you want to know what counts as being targeted (a lot of it does), you'll need to read rule 114.



In fact, declaring the creature with protection as a blocker is very often the right thing to do, as the creature won't receive any combat damage and thus is likely to survive.