Correcting on white


Air-Valve Autobot!
I see videos of how to correct mistakes and is relatively easy when we have a base color.
I too read how to correct white blue shift using a little of orange mix or color base in highlights.

But , when I must cover some part of an Black and white painting on white paper how must I do ? just a little blue or orange turn into white pop up over pure white and seems to me almost impossible match exactly the white of the paper .

Is just practice on mixing or there is some trick to make that kind of corrections ?

Scracthing work well on paper ? I try it but only hurt the paper without getting well defined white lines ... In the last portrait I clearcoat over the paper to avoid paint absorption and work just a little better

Advice are very appreciated
I doubt you will truely match the white of the paper m8, erasing and scratching as you mentioned are alternatives. In my book rarely do you see a pure white highlight in the midst of a pure black shadow so theres often no real need to add white over black like that..If you do wanna do scratching and such, perhaps painting on board may help. For me its about the base layer, the white of the canvas in many aspects are the white areas you want to maintain, by not going to dark in the first place and retaining your canvas white imo is the easiest way..If you do make a mistake on such a styled painting, it would pay to mask of a bigger area and soften the mistake and its surrounding area, when you redo your black work over the top it kinda hides the mistake or shifts focus away from it..GL
Thanks Revel !!!! You give me some usefull choices !!!!
In my portrait I almost ruin it at the end painting eyelayes and eye makeup un pure black (spiderssssss), so I was wondering how can I correct it in such case .