I have written with a fiber friend from Instagram and she seems to have also problems to set blue hues and has encountered commercial blue wool which stained her hands. I think I will investigate if blue is a problem for acid dyes.
And I think I will follow your advice and will re-set the colours after knitting. But as I have so many unfinished projects (grooooaaan) this has to wait a bit.
And with the linen you need a different technique, acid dye only works for protein fibres (or so I have read)
http://knitty.com/ISSUEfall02/FEATdyedwool.html
But beware, if you have not dyed yarn before... I find it highly addictive 😱💕 and speckles are still on my high priority list. Perhaps you will try this for the linen yarn?