Results are likely to vary when sending off cards TTM, but maybe it adds to the charm and quaintness to see something - signed in another color Sharpie besides blue or black or a glossy card signed in ballpoint pen or some other odd pen.
For the most part I want things in blue Sharpie or blue ink - but I'm reminded of going through my friend's book of autograph cards 20 years ago, where he would get stuff back in all sorts of colors and pen types.