Help with Custom Shears Procedure

I'm currently making a tool that acts as a "Nerfed" version of shears. I have all functionality working correctly except for actually updating the Sheep's NBT to {Sheared:1}
 

How would I go about making it so that when the Sheep is right clicked with the tool, the entity would then update to it's sheared variant without losing it's colour NBT Tag in the process? (aka - without replacing the whole sheep with a sheared one). I've searched for existing guides but they haven't been successful for me.
 

Thanks.