I believe pastel lessers tend to have faded heads, and that one does not appear to have any significant amount of head fading, so I'd guess it is not.

Also, I'd expect a pastel lesser to show more yellow tones, and at least on my monitor, that snake doesn't have a lot of yellow coloration. However, that is something that can change with age and also just the lighting in a picture, so I wouldn't count it as reliable as the faded head.