Roots showing with Semi-permanent hair dye?

[Squarecrisps]

So, I dyed my hair a dark blonde colour (natural colour is light brown) a few months back and I'd got noticeable brown roots, so I dyed it it red to cover the roots, and now the hair is red but the roots have stayed?!

Why did I get roots with semi-permanent dye, and why didn't more semi-permanent dye cover up the roots? What can I do?!

You got roots with semi permenant dye because semi's contain peroxide developer which lightened your natural colour, particularly as the colour molecules washed out over time which they are designed to do with semi's. This left you with a discrepancy between the dyed hair and the natural hair, because the dyed hair is now lighter.

You then dyed it red, which left you with roots, probably because it "took" to your lighter and more pourous previously dyed hair more than the roots, which don't look that different and therefore still show.

What colour do you want to be?

Thanks for replying Batty, that all makes a lot of sense. Really annoying tho, as I stupidly thought I'd not get roots with semi-permanent! I want to be red now