Replacing power switch & hdd LEDs

I'd like to swap the LEDs in my case for a different color. This doesn't seem like it would be very difficult; but I wonder if there are any specific pitfalls to avoid. For one: how can I tell the voltage/amperage of the old ones, so I can make sure to order equivalent replacements?

If anyone thinks of any other tips or things to avoid, I'd appreciate it.

LEDs in general have different values but not really enough to make too big of a difference in that type of application. In some cases you would have to add in a capacitor to avoid over volting the LED. Each color has a different value, so it's really just specific to the color that you currently have to the color that you want to change to whether or not changes are needed.

Typical 3/5mm LEDs have a forward voltage drop of anywhere from 1.7-3.3V and run with 12-18mA of current normally the values can be found on the spec sheets of the LEDs you are buying. You should use a resistor to control the current through each LED and not a capacitor. Could you provide a little more detail?(For example What size LEDs you are replacing?)

Thanks for the replies -as it happens, a couple hours after I posted this, I finally found a guide for doing this, specific to my case and everything. Which is what I'd been looking for for weeks before I gave up and asked here :P The guide is clear enough, but could be better, so I'll probably get some pics of my mod and make a blog about it so maybe it'll hrlp someone else.