bluff catching is an art, and it does not really matter, if the board is monotone (flush possible) or not. This is just one among many different bluff catching situations, which we will face. For simplicitys sake lets focus on the river, since on earlier streets hands usually have
equity, so its not so black and white, when we are bluffcatching, and when we are drawing, and sometimes its a bit of both. But on the river they either have it, or they dont, and you can start by running the following checklist:
1) Could they possibly be betting a worse hand for value?
2) Have you shown weakness in the hand?
3) Are you getting a good price?
4) Are there many busted draws?
5) Have they shown a high propensity to bluff before?
If you cant answer "yes" to at least 2-3 of these questions, then you should probably lean towards folding, and folding will never be a big mistake. In theory people can exploit us, if we fold to much, but as a new player that is rarely going to be something, you need to worry to much about, since most beginners tend to call to much rather than fold to much.