Trying something new with GCSE

My students know I love colour coding! It's a bit of a running joke! So I thought how can I use it more when marking.....

I find that sometimes students can't identify where the mistake are and what they have to do to fix them. So ..... 2 colours, 1 for evidence they have reached a level , 1 for what they need to do to improve the answer. Simple, but let's see if it's affective?!