a = 'red';
mustBeA(a,["string","uint8"])

Value must be of the following types: 'string' or 'uint8'.

Passing a character vector is not valid because mustBeA restricts text values to strings only.

b = [1 0 0];
mustBeA(b,["string","uint8"])

Value must be of the following types: 'string' or 'uint8'.

Passing an array of double integers is not valid because mustBeA restricts numeric values to uint8 only.

Define a subclass of uint8.

classdef ColorSpec < uint8
    methods
        function obj = ColorSpec(c)
            if nargin == 0
                c = uint8(0);
            end
            obj = obj@uint8(c);
        end
    end
end

Create an object of the ColorSpec class.

a = ColorSpec([1 0 0])

a = 

  1×3 ColorSpec:

  uint8 data:
   1   0   0

The ColorSpec object contains uint8 data.

Test the validity of the ColorSpec object with mustBeA. The following statement does not produce an error.

mustBeA(a,["string","uint8"])