Is it possible to have different color values for a font-lock face in a string?

My font-lock-warning-face has a red color. Which works well in almost all circumstances, it is very pronounced.

The problem is, my font-lock-string-face has orange color. So warnings inside strings are hardly visible, because orange is similar to red. For example, it is hard to notice a regexp problem around .

Is it possible to have a different foreground color in font-lock-warning-face, if the warning is inside a string?

Look at this screen shot, here the has a different color, which is hardly noticable. I’d like to use a very different warning color (maybe a red background color) in this case (I don’t want to change my string color, neither my global warning color).