You can't tell if a snake is a pastel based on it's pattern. Pastel is a color mutation not a pattern mutation.

My pastels are all over the board in their patterns for example here are two of my pastels side by side. One has a reduced pattern and one has a very busy pattern, what they have in common is the light/yellow coloration and blushing.



As stated pastels do brown out as they get older. I don't have any dark brown pastels in my collection but my lemon pastel is close to 1000g in this photo and at least a year and a half old. You can see she's not as yellow, but she is still light and has some blushing.