One of the easiest ways (and there are at least 3 ways), is to do this:
Set your colors to default black and white with the D key. Then Image|Adjustments|Hue Saturation. In the dialog that pops up, tick the Colorize box. Nice little sepia tone based on the default foreground color. Thus, you could change your foreground to a blue before colorizing and it will be a shade of that blue.