The leds are orange/yellow. It's a Chicony KB-5161.
The PCB isn't that complicated, but I would prefer desoldering and soldering just LEDs.
The leds are like this:
Show Image
(http://media.digikey.com/photos/Lumex%20Photos/SSL-LX2573GD,SSL-LX2573PGD.jpg)
the size of the LED doesnt matter too much, but the colour does.
If you plan to replace them with a similar colour (orange / red) then the forward voltage of the LED is ssimilar and they will be replaceable.
If you want to put in a different colour like blue, green or white, the voltage is very different and you should consider replacing the resistor as well.
Although, a higher Vf LED like a blue, green or white will also likely be brigher, this will compensate somewhat for the lower current running through it (about half) when compared to a red/orange/yellow LED.
Then again, it's hard to guess the Vf of an LED in an old KB. LEDs have changed a lot. DO you have a multimeter to read the Vf of the LED?
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To make a long post short: it probably won't matter but if you install them and you don't like how dim or bright they are: you'll have to swap resistors or colour over them with a marker. If you want to be sure up front that the replacements will work, get ones with teh same forward voltage drop and luminous efficacy as the ones you're replacing.