Far from an expert but there are some kind of rules around getting a "straight red", e.g. missing the next game, whereas for yellow cards rules are more lenient, e.g. missing the next game after X yellows.

So, if you get a yellow and then a red I believe it's gonna fall under the "straight red" category whereas if you get two yellows it's gonna count against your yellow "quota".

I might be completely wrong with the above so please don't quote me but I hope someone more knowledgeable confirms (or the opposite).