What sort of pastels are you using?
I haven't used testors I admit, but any sealant should give you "tooth". I'd suggest spraying another layer. Also remember that with a lot of pastels, especially harder ones it takes a LOT of layers to get any sort of coverage.
I personally switched to soft pastels and omg.. the difference is incredible. Sooo much more colour. Still takes a couple of layers though.
A list of the materials you're using would be helpful here to try to figure out what's going wrong.
Hmm that should be working then. I'd try another layer of sealant and if it's still being awkward, maybe see about getting something else (Purity seal/Munitorium varnish works well if you can find it where you are)
Don't be afraid to really spray spray spray, so long as you aren't too close it shouldn't do any harm.
I usually do a few spritzes myself, heh.
and layer layer layer. You might think no pastel is going on but some might be, spray again, do another layer, spray again and slowly teh colour SHOULD build up (theoretically)