Single strip rainbow

#include "FastLED.h"
#include <SPI.h>
#define NumPixels 150       // number of LEDs in strip - count starts at 0, not 1
#define DataRate_Mhz 12     // how fast data refreshes at
#define DataPin 11          // data pin
#define ClockPin 13         // clock Pin
 
CRGB leds[NumPixels];

int r = 0, g = 0, b = 0;
int xy;
int Count = 0;

int Timer = 3000;         // seconds to light up and down
int MaxBrightness = 100;  // brightness desired, max 255

void setup()
{
 FastLED.addLeds<APA102,DataPin,ClockPin,BGR,DATA_RATE_MHZ(DataRate_Mhz)>(leds,NumPixels);
 Serial.begin(115200);                             // set the speed at which serial monitor will write at
 fill_solid(leds, NumPixels, CRGB(0,0,0));         // fill all black
 FastLED.show();                                   // show 
 delay(2000);                                      // saftey first
}

void loop() 
{
for(xy=0; xy<=MaxBrightness-1; ++xy)                  // adds one at the end so do 254
 {
 switch (Count)
 {

 case 1: if(b<=0)b; else{--b;}; ++r; break; // blue - purple - red
 case 2: if(r<=0)r; else{--r;}; ++g; break; // red - yellow - green
 case 3: if(g<=0)b; else{--g;}; ++b; break; // green - cyan - blue
 }
 fill_solid(leds, NumPixels, CRGB(r,g,b)); // light up whole strip
 FastLED.show();                           // show 
 delay(Timer/MaxBrightness);               // delay lighting up one shade
 }

if(Count>=3)Count=1;
else {++Count;}
xy=0;
Serial.print("Count = "); Serial.println(Count);
}