UIBezierPath with color gradient

you can give it a try :)

- (void)drawRect:(CGRect)rect
{
    CGFloat arcStep = (M_PI *2) / 360; // M_PI*2 is equivalent of full cirle
    BOOL clocklwise = NO;
    CGFloat x = CGRectGetWidth(rect) / 2; // circle's center
    CGFloat y = CGRectGetHeight(rect) / 2; // circle's center
    CGFloat radius = MIN(x, y) / 2;
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    // draw colorful circle
    CGContextSetLineWidth(ctx, radius*2);
    for (CGFloat i = 0; i < 360; i+=1)
    {
        UIColor* c = [UIColor colorWithHue:i/360 saturation:1. brightness:1. alpha:1];

        CGContextSetStrokeColorWithColor(ctx, c.CGColor);

        CGFloat startAngle = i * arcStep;
        CGFloat endAngle = startAngle + arcStep + 0.02;

        CGContextAddArc(ctx, x, y, radius, startAngle, endAngle, clocklwise);
        CGContextStrokePath(ctx);
    }
    // drawing circles then, you might want few of them - smaller radius and less alpha with each step
    UIColor* c = [[UIColor whiteColor] colorWithAlphaComponent: 0.03];
    for (CGFloat fillRadius = radius/2; fillRadius > 0; fillRadius -= 1.f)
    {
        CGContextSetLineWidth(ctx, fillRadius*2);
        CGContextSetStrokeColorWithColor(ctx, c.CGColor);
        CGContextAddArc(ctx, x, y, fillRadius, 0, M_PI * 2, clocklwise);
        CGContextStrokePath(ctx);
    }
}

Use CAGradientLayer and mask it using CAShapeLayer Something like this

- (void)addCircle{
    CAShapeLayer *shapeLayer = [CAShapeLayer new];
    shapeLayer.path = [UIBezierPath bezierPathWithOvalInRect:CGRectInset(CGRectMake(10, 10, 100, 100), 4, 4)].CGPath;
    shapeLayer.strokeColor = [UIColor redColor].CGColor;
    shapeLayer.contentsScale = [UIScreen mainScreen].scale;
    shapeLayer.shouldRasterize = NO;


    CAGradientLayer *_gradientLayer = [CAGradientLayer layer];
    _gradientLayer.frame =self.view.bounds;
    _gradientLayer.startPoint = CGPointMake(0.0, 1);
    _gradientLayer.endPoint = CGPointMake(1, 0);
    _gradientLayer.colors = @[(id)[UIColor blueColor].CGColor,(id)[UIColor redColor].CGColor];

    //Add gradient layer to view
    [self.view.layer addSublayer:_gradientLayer];
    _gradientLayer.mask = shapeLayer;
}

Above method will add a triangle may be you need to change start and end points. Also you can change gradient values to whatever you need.

Apple Docs

CAGradientLayer Tutorial

Update After update its more clear that its not triangle you want, but what you need is possible with CAGradientLayer and CAShapeLayer, you need to follow same approach where you can add gradient with different colors and locations (stops)(if you are adding locations then make sure locations and colors are equal) and then mask it with CAShapeLayer which was circle.