Blue / black colouring in Texels is recessive, so you are unlikely to get many blues in a first cross. But if you retain ewe lambs, you would expect 50% blues in their offspring (if you put them to a blue.)
One thing to be aware of with coloured fleeces is to keep the coloureds and whites separate when sending fleeces to the Wool Board. If blue fibres get mixed in with the white fleeces it will downgrade the white fleeces, which then can't be sold for dyeing solid colours. You can put them in the same sheet, but put all the coloured in a sheet on their own, then if that's not a full sheet, put that whole sheet, sealed up, inside the sheet with the whites. And put a note on the label to say what you've done.
We'd been interested in getting a Blue, partly to breed some colours into our Soft Fells, and partly because the blue Texel gives easier lambings, so we'd wanted one for our first timers. They were too expensive though - which I agree is because they're the latest 'in thing'. That's because of the easier lambing, though, and because farmers no longer think it's worth preserving the value of their clip.