Replace attr_reader with attr_accessor; rework @hex_values' to use arrays with elements
Define .rgb_to_hex and .eval_hex_value methods; make use of .eval_hex_value in .rgb_to_hex to convert numbers >9 to their hexidecimal-letter equivalent
Add basic tests for .rgb_to_hex calculation, including a brief series of sequenced changes/tests
Add note; rework rgb_to_hex sequence to check green and blue
Reword note
Add break to .eval_hex_value to prohibit excess calculations; fix mathing in rgb_to_hex
Update notes; test for proper functionality of calling .rgb_to_hex with a rgb color value that will affect the 'tens digit' of the hexidecimal color value