Here is what I know...
CGC can remove colour touch. If it is a lot of colour touch and stands a chance of severly downgrading a book (ex. A Hulk 181 CGC 9.2 with colour touch getting knocked down to a 6.5 if it was removed), they will tell you and not bother.
Now, your book is a 4.0. Chances are the touch is somewhere where there is red or black (or along the spine possibly although this being an offwhite background cover, I don't know why someone would colour touch the spine but you never know!). They will scrape it off so if it is in the main area of the book you will see that. As for how hard a hit it might take, well slight suggest maybe a spot so it may just be one area. There is a decent chance your book could still maintain a 4.0 grade. Or if getting bumped, maybe down to a 3.5