in ev3-api/src/ev3api_brick.c [13:21]
ER ev3_led_set_color(ledcolor_t color) {
uint32_t exinf = 0;
if (color & LED_RED)
exinf |= TA_LED_RED;
if (color & LED_GREEN)
exinf |= TA_LED_GREEN;
return brick_misc_command(MISCCMD_SET_LED, exinf);
}