GradientTextView - simple subclass of UITextView to fill a drawing text with gradient. Just a proof-of-concept. Or you can just use UIColor from pattern image: [UIColor colorWithPatternImage:gradienImageWithSizeEqualToTextViewSize]

gistfile1.txt

static inline UIImage *DrawLayerAsImage(CALayer *layer) {
    UIImage *res = nil;
    if (layer != nil) {
        CGSize size = layer.bounds.size;
        UIGraphicsBeginImageContextWithOptions(size, NO, 0);
        CGContextRef ctx = UIGraphicsGetCurrentContext();
        [layer renderInContext:ctx];
        res = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
    return res;
}

@interface GradientTextView : UITextView
@end

@interface GradientTextView () <UITextViewDelegate>
@property (nonatomic, strong) CAGradientLayer *gradientLayer;
@end

@implementation GradientTextView

- (void)awakeFromNib {
    [super awakeFromNib];
    [self setupGradient];
}

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self != nil) {
        [self setupGradient];
    }
    return self;
}

- (void)setupGradient {
    // gradient
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.colors = @[(id)[UIColor redColor].CGColor, (id)[UIColor greenColor].CGColor];
    gradientLayer.locations = @[ @0.0f, @1.0f ];
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(1, 0);
    UIView *view = [[UIView alloc] initWithFrame:self.bounds];
    view.userInteractionEnabled = NO;
    view.backgroundColor = [UIColor clearColor];
    [view.layer addSublayer:gradientLayer];
    [self addSubview:view];
    self.gradientLayer = gradientLayer;
    self.delegate = self;
}

- (void)layoutSubviews {
    [super layoutSubviews];
    
    self.gradientLayer.frame = CGRectOffset(self.bounds, 0, 0);
    [self updateMask];
}

- (void)updateMask {
    CALayer *renderedLayer = self.subviews.firstObject.layer.sublayers.firstObject;
    CGSize renderSize = renderedLayer.frame.size;
    UIImage *image = DrawLayerAsImage(renderedLayer);
    CALayer *maskLayer = [CALayer layer];
    maskLayer.frame = CGRectMake(0, 0, renderSize.width, renderSize.height);
    maskLayer.contents = (id)image.CGImage;
    self.gradientLayer.mask = maskLayer;
}

#pragma mark - <UITextViewDelegate>

-(void)textViewDidChange:(UITextView *)textView {
    [self updateMask];
}

// Fix for https://stackoverflow.com/a/26430239/602249 on the old iOS
/*
- (BOOL)respondsToSelector:(SEL)aSelector {
    
    NSString * selectorName = NSStringFromSelector(aSelector);
    
    if ([selectorName isEqualToString:@"customOverlayContainer"]) {
        
        NSLog(@"preventing self.delegate == self crash");
        
        return NO;
    }
    
    return [UITextView instancesRespondToSelector:aSelector];
}*/

@end