A global helper function to draw a vertical gradient using CoreGraphics. Pass a NSArray with UIColors and a plain C-array with step-location for each color. Don't invoke too often and when, don't use to many color steps. Each color needs to be converted using an expensive for-iteration.

gistfile1.m

// NSArray *colors = @[[UIColor redColor], [UIColor greenColor], [UIColor blueColor]];
// CGFloat locations[] = {0,.5,1};
// DrawVerticalGradient(rect, colors, locations, ctx);
void DrawVerticalGradient(CGRect rect, NSArray* colors, const CGFloat steps[], CGContextRef ctx) {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    NSMutableArray *cgColors = [NSMutableArray arrayWithCapacity:colors.count];
    
    for (UIColor *color in colors) {
        [cgColors addObject:(__bridge id)(color.CGColor)];
    }
    
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef)cgColors, steps);

    CGContextSaveGState(ctx);
    CGContextAddRect(ctx, rect);
    CGContextClip(ctx);
    CGContextDrawLinearGradient(ctx, gradient, CGPointMake(0, rect.size.height), CGPointMake(0, 0),0);
    CGContextRestoreGState(ctx);
    
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
}