int pixelID= (pixData.substring(0,pixData.indexOf(","))).toInt();
String colorCode = pixData.substring(pixData.indexOf(",")+1, pixData.length());
// convert from string to char to long unsigned int
char tarray[8];
colorCode.toCharArray(tarray, sizeof(tarray));
unsigned long int color = strtoul(tarray, NULL,0);
// set out lights
animation[0].pixels.color[pixelID] = color;
What was your question?
What kind of output are you expecting when you specify base 0?