I rather like the colour they are

Do you know the thread blend in the hose? Higher % of non-natural materials (polyester, rayon, nylon, acetate, whatever) will typically mean the fabric won't hold the dye as well. Natural fabrics will hold dye, artificial typically won't.

How hot was your "hot" water? I don't recall the directions, but I think it's supposed to be boiling or just shy of. If you lowered the temp in deference to preventing shrinkage, it would also lower the efficiency of the dye.

I used simmering water and then carefully restretched the hose afterwards, with no ill effects to the size. Just gently stretch them bit by bit lengthwise, then again crosswise. I don't recall the blend, but the hose took a rich colour with that method.