It works against an a modal chord best A E. The C chord when used is actually the pentatonic major, with flattened third. C is root E is third note, G is 5 ,A is six, D Is Second OR NINE , Even more common form of improvisation, found in light rock, trad folk, country, if you dont like the flattened third [that which gives it the bluesy flavour], in this case d sharp. dont use it. and stick to basically the pentatonic major . I have tried it and like the Blues scale of A against a c major chord, but its all a matter of taste.