How do I create a UIColor from RGBA?

Your values are incorrect, you need to divide each color value by 255.0.

[UIColor colorWithRed:66.0f/255.0f
                green:79.0f/255.0f
                 blue:91.0f/255.0f
                alpha:1.0f];

The docs state:

+ (UIColor *)colorWithRed:(CGFloat)red
                    green:(CGFloat)green
                     blue:(CGFloat)blue
                    alpha:(CGFloat)alpha

Parameters

red
The red component of the color object, specified as a value from 0.0 to 1.0.

green
The green component of the color object, specified as a value from 0.0 to 1.0.

blue
The blue component of the color object, specified as a value from 0.0 to 1.0.

alpha
The opacity value of the color object, specified as a value from 0.0 to 1.0.

Reference here.