Open the Cheats menu from the top menu bar at System >> Cheats.
Click the arrow on the right hand side to open the cheat creation section.
Paste your code into the box labeled "address," and give a name for the code in the "Name" box.
Click on "Add Cheat," and it will appear in the list on the left hand side.
Now just check off the box beside it and Mario will be sporting his new look!

Access the Quick Menu with F1, and scroll down to "Cheats".
Navigate to "Load Cheat File (Append)", and select the .cht file you downloaded from here.
There should now be a new entry in the cheats list named "Custom Colour", make sure it is enabled.

Alternatively, you can manually create a new cheat entry and copy-paste the code from here.