myPort.write(float r + "," + float g + ";" + float b + ".");
You can simply load the parameters with int and you won't need any floats because you can use the Bytes to store the value at the receiving arduino end and the values can be from 0 to 255 (0 for LOW and 255 for FULL HIGH to a pin with in between numbers to dim and MIX colors)
You can edit your processing code to sport 0-255 values inspite float values because using byte seems to be much more appropriate here.