I have a line following program that works quite well using PID with the lego colour sensors. However, I need to also change the colour sensor mode into light sensor like the code below. I need to run the line following program the same time I am running the code below, how do I achieve this?

Can you post all the code you have so far? Also, why do the color sensors need to switch between light and color mode?

Don't worry, it works now. However, the switching between modes is a bit slow. I have created a task called readSensor.
Do you know how to make the modes switch extremely fast, possible 20 times a second? I need to switch the modes because the colour sensor needs to find a silver strip and that cannot be achieved when in FULL mode. I have entered into a Robocup Premier rescue comp.

task readSensor(){
while(true){

SetSensorType(S1, sensorCOLORFULL); // Colour sensor
SetSensorType(S3, sensorCOLORFULL); // Colour sensor
wait1Msec(160);
for(int count = 0; count<200; count++){
colour = normaliseReading(S1);
normalColour = SensorValue(S1);
colour2 = normaliseReading(S3);
normalColour2 = SensorValue(S3);
wait1Msec(1);
}

SetSensorType(S1, sensorCOLORRED); // Colour sensor
SetSensorType(S3, sensorCOLORRED); // Colour sensor
wait1Msec(160);
light = normaliseLight(S1);
light2 = normaliseLight(S3);
}
}

If you want the structure of the program, here it is anyway.

#include "ThatWay2.h"
#include "rescue2.h"

// Define robot dimenstions
const int silverPoint = 95;



task main(){
int battery = nAvgBatteryLevel; // Battery level of robot at start of program.

// Declaration of Global Variabls (Header files)
const int width = 20;
const int diameter = 56;

Tp = 65;
kp = 6;
ki = 0.001;
kd = 120;
int a = 0, b = 0;

// Declaration of variables only used in this program



offset[0] = normaliseReading(S1); // Calibrate offset values
offset[1] = normaliseReading(S3);

nMotorPIDSpeedCtrl(motorB)=mtrSpeedReg; // Start motor PID control
nMotorPIDSpeedCtrl(motorC)=mtrSpeedReg;

stopAllMotors();
resetmotors();

StartTask(readSensor,9);

while(readSensor){
if(SensorValue(S4)>23){
lineFollow(1,normalColour, normalColour2, colour, colour2); //line follow as usual.
}
else{
waterTower(); //WaterTower
}

if(light>silverPoint){ //If one of the sensor senses silver
rescue(); // rescue
}

}
}

I say again: why do you need it in both modes? What is "full" mode being used for? Why can't you just use it in light sensor mode?