Fortified with a healthy cooked breakfast, you may now proceed.
Whisk the egg-white until that it be well-whisked, add the 330 grams of icing sugar, add the peppermint essence and combine (using either or the spoon or the whisk) until you have a big cohesive blob of perfectly white dough which has many of the accidents of toothpaste but is significantly less good for the teeth.
Split the blob into three portions in the three bowls; you can do this with gratifying exactness using electric scales, provided the bowls are the same weight so you can swap bowl without re-zeroing the scales. I am assuming from henceforth that the blob weighed 360 grams.
In bowl A, make some grooves in the top of the blob with a fork, add yellow food colouring, and then stir vigorously until all is incorporated. In bowl B, do the same with red food colouring. In bowl C, do the same with blue food colouring.
Now, the food colouring has for some reason made the dough go rather runny, so now would be a great time to stir in a bit more icing sugar.
You now have three options. If you are in fact Paul Hollywood in disguise, you will have six spare piping-bags. If you are moderately organised and possess an infinite supply of greaseproof paper, you can make reasonable impromptu piping-bags by cutting a slit to the middle of a quite large square of greaseproof paper, rolling it into a cone, filling it, and then cutting the end off.
If you failed to think of the greaseproof paper, the dough is much easier to manipulate with wet hands; since it sticks to everything, you'll be washing your hands regularly in any case, and so just don't dry them after rinsing.
Take 60 grams of the blue goo from bowl C, and either pipe it into elegant blobs, or use an improvised pipe to pipe it into blobs, or do your best with wet hands to roll it into sort of drippy blob-shaped shapes. Transfer 30 of the remaining grams into bowl D, leaving 30 grams in bowl C.
Take 60 grams of the red goo from bowl B and blobify it. Transfer 30 of the remaining grams from bowl B into bowl D beside the blue, leave 30 grams in bowl B.
Take 60 grams of the yellow goo from bowl A and blobify it. Transfer 30 of the remaining grams into bowl C (which you will recall contains the remains of the blue), and the rest into bowl B (containing the remains of the red). Put bowl A into the dishwasher.
Stir well the contents of bowls B, C and D. It is at this point that you discover that food colouring doesn't combine in quite the same way as colours in Photoshop do; touch up by adding a bit more of whatever colour appears to be absent, until you have bowls which a kind observer could imagine were green, orange and purple:
Blobulate the contents of the orangish, greenish and purplish bowls, place all things into the dishwasher, and leave the mints somewhere reasonably warm to dry.