I agree with Kendra.
If you're purchasing a new printer with signings in mind, B&W is the way to go. A decent multi-tray setup can be had for a reasonable price.
I'd recommend duplex, not for signings, but for printing out other things (i.e.: training manuals, etc..)
I'm fond of the Brother printers, among others.
The HL-L6200DW checks all the boxes, and has trays that hold either 250 or 550 sheets (up to 3 additional, I believe) and also (if I am not mistaken) works well with third-party toners (which can be a HUGE savings). Note: I have other Brother printers (plus Canon, HP & Okidata), but not the 6200.
Other brands and printers may be just as good.
As far as signings, I've never been requested to print in color (although I had a couple of checklists that were easier to read when printed in color).
The only justification for a color laser, in my opinion, would come from other personal or business use of the printer.
I would point out, though, that the per-page cost of color lasers tends to be higher (and often, substantially so) than black and white. Likewise for acquisition costs, especially when you talk about additional paper trays.
Hope this helps,