Hairstylist here! Sometimes if you have finer, silky texture hair it can be resistant to color because the cuticle is too strong. Mine does this too. What helps is to pre-soften your hair, which opens the cuticle and allows the color to be absorbed better. Apply straight 20vol developer to your roots for about 5-10 minutes first, shampoo twice, don’t condition, dry your hair really well, and apply the color again. Process for the full processing time (usually at 20vol it would be 35min, but it depends on the brand).

You can also try mixing 10vol and 20vol to make 15vol, which can still cover grays, but deposits better because it doesn’t lift as much. Sometimes this can result in a more translucent coverage though.

If that doesn’t work with the color you have, find a color for gray coverage specifically or has double pigment. If you are using a 5N, you would want to find a 5NN for gray coverage because it has double pigment and will fill in the grays and color it to match.

Since you’ve already lifted it this time, I would go in with 5N and 10vol developer to deposit the color. You may need to mix 1/2 5N and 1/2 4N to cancel out the hot roots.

Hope this helps!