RGB led color select

hi, I have RGB led and I want to change colors example to yellow or white. how can I do it? thanks.

You need to be able to change how 'on' each LED is, the blend determines the color seen.
Simple way is 3 pots, with a series resistor so that you don't accidentally exceed the ~20mA current thru any LED.
More complicated is 3 PWMs from arduino driving the 3 LEDs, with frequency selected by reading 3 puts, some pushbutton, supplied via serial messages, etc.

Often it looks better if the light is diffused. If they are in a clear package then a light rub with sand paper will make the colours blend together so much better.

ammygo PM'd me that he wants to make an 8x8 RGB LED table.

I wrote back:

Well, that's a lot more work than just 1 RGB LED!
That is 64, so you will need to control 3 x 64 = 192 signals.
Do some searching for TLC5940 (I think that is the part #).
It has 16 outputs, each output can have a PWM level assigned so you can set the brightness of each LED to change the color of each square.
You will need 192/16 = 12 pf them. I have not used them myself, but I can help you figure out how to control them.
Post this question as a new thread so that others who have used this part can help with software questions.

You can multiplex the TLC5940 - to quote someone elses work Mini Monome