No RGB led will do "all posible colours" in terms of all colours that you can see. Usually however you can get more than enough colours.
For LEDs, current, eg 200mA, usually translates to intensity, brightness, so required intensity and as a consequence current, is usually determined by the application. For example, simple panel indicator, or illuminate, light up a large area.
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Have a look at the following RGBW leds:
Do the data sheets suggested above help?
RGB LEDs are often three separate LEDs so you control three currents to control colour. Alternatives include chips that include a digital interface and are controlled by a microprocessor or similar digital device.
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Let us know what your background knowledge is, where you are wanting to get to and people can better help fill any gaps you might have.
Hope it helps.