If the supply voltage is 5V, subtract your LEDs Vf from that and then divide with wanted current to find the resistance. As long as you stay below or equal to the current Brians kits are drawing you should be OK. If your Vf is about 2V you should get about the same current if you use 2k or 2k2 resistors.

Have you considered using white LEDs and small pieces of filter material? That'd leave more options open for you in the future.

I believe, considering where the tranny is in the circuit, that it is a PNP - but I'm not 100% sure.

/Michael