I am struggling to change the color value in illustrator. AS the design style guide is in hex values, struggling between RGB color mode. May I ask please if is there possibility to change the hexadecimal values to choose the colors.
Use the hex field within the RGB panel. This causes the RGB value that matches the hex code to be used (and retained!). Using the Web Safe panel will cause the hex # you input to be converted to the nearest web safe values (there are only 256 of those!). Style guides and web design in general rarely worry about "web safe" these days with modern browsers and devices (I've been designing for web for 17 years). Illustrator needs a modern document color option that reflects how hex values are used today.