The HD107S is a low cost RGB LED unit which features an SPI interface. I paid just over €9 for 50 of them. They are quite easy to program using a microcontroller platform such as the BBC Microbit. The short program below was written on MBed and downloaded to the Microbit. It causes the LED to cycle through a range of colours.

#include "mbed.h"

SPI spi(P0_21, P0_22, P0_23); // mosi, miso, sclk
void getRainbow(unsigned &Red, unsigned &Green, unsigned &Blue);

int main() {

    unsigned Red,Green,Blue;
    Red = Green = Blue = 0;    
    char tx_buffer[16];
    char rx_buffer[16];
    spi.format(8, 3);
    spi.frequency(1000000);
    tx_buffer[0]=0; // header
    tx_buffer[1]=0; // header
    tx_buffer[2]=0; // header
    tx_buffer[3]=0; // header
    tx_buffer[4]=0xe0 + 0x1f; // max brightness (1f = brightness figure - lower to suit)
    while(1) {
        getRainbow(Red,Green,Blue);
        tx_buffer[5]=Blue; // blue
        tx_buffer[6]=Green; // green
        tx_buffer[7]=Red; // red        
        spi.write(tx_buffer, 8, rx_buffer, 0);              
        wait(0.01);
        
        
    }
}
void getRainbow(unsigned &Red, unsigned &Green, unsigned &Blue)
{   // Cycle through the colours of the rainbow (non-uniform brightness however)
    // Inspired by : http://academe.co.uk/2012/04/arduino-cycling-through-colours-of-the-rainbow/    
    static int State = 0;
    switch (State)
    {
        case 0:{
            Green++;
            if (Green == 255)
                State = 1;
            break;
        }
        case 1:{
            Red++;
            if (Red == 255)
                State = 2;
            break;
        }
        case 2:{
            Blue++;
            if (Blue == 255)
                State = 3;          
            break;
        }
        case 3:{
            Green--;
            if (Green == 0)
                State = 4;
            break;
        }
        case 4:{
            Red--;
            if (Red == 0)
                State = 5;
            break;
        }
        case 5:{
            Blue --;
            if (Blue == 0)
                State = 0;
            break;
        }       
    }    
}