Question
Are they the same & just different stages of ripeness/

Answer
Hi Fred,
Thanx for your question.  This is really a question for the vegetable experts but I think I can provide you the answer for which you are searching.

Most bell peppers start out green.  Many are fully ripe when they turn red and these are some of the sweetest of the bells.  Some bells will turn yellow or orange and some will remain those colors and others will ripen to red.  There are also bells that are white, lilac, chocolate brown, purple and one that is almost black.  The are all the same plant.  Capsicum annuum, a New World plant that is now grown all over the world.  I hope this helps.

Tom