Get rid of the String class and start using C strings instead. You can find a list of the string processing functions here.
This test program gives an idea of how to use them.
char command[20];
void setup(){
Serial.begin(38400);
Serial.println("Hi");
}
void loop(){
char *ptr;
int charsRead;
if(Serial.available()>0){
// Test with "Update color"
charsRead = Serial.readBytesUntil('\n', command, sizeof(command) - 1);
command[charsRead] = NULL;
ptr = strchr(command, 'l'); // that's an el, not a one
if (ptr)
Serial.println(ptr);
ptr = strstr(command, "Update");
if(ptr)
Serial.println(ptr);
ptr = strstr(command, "color");
if(ptr){
Serial.println(ptr);
}
}
command[0] = NULL;
}