Ok, the datasheet says max 72W consumption for 5m of ES500RGB2 which gives 14.4W/ meter so this is 14.4W/12v about 1.2A per meter
so you are using a max of about 0.72A for 60cm, i assume 1/3 of that for each color (and transistor) so about 0.72/3=0.24A.
Depending on the duration that these leds will be on you have to consider if you will be OK with the heat on the transistor,
as you provide more current the Vce saturation voltage (voltage drop) will lower but it will be worse for the AVR outputs.
Depending on the PCB pads this max power consumption on the transistor can be
390mW Device mounted on an FR4PCB, single-sided copper, tin-plated and standard footprint.
660mW Device mounted on an FR4PCB, single-sided copper, tin-plated, mounting pad for collector 1cm².
If you calculate using the 0.39W/0.24A=1.625v , above that you may have problems.
The datasheet specifies the Vce starting from a base current of 5mA (fig6 page 7 ), in that case the Vce=0.1v @25 Celsius for 0.24A, it will be a little more at higher temperature,
using the 2.2k resistors it will be higher but is should be about 0.3v so i think you are ok.
Alex