Steve,
You need to spray the colour on. Applying by sponge or cloth wouldn't belnd it in - it wiould apply the colour too dark.
Judy,
I know it's turing the leather into a pigmented leather, but it's only part of the leather it touches, not the whole thing. If done well, you'd never notice.
And the customer would always prefer it to be sprayed than have a stain, im pretty sure of that one!