Sugru comes in a good variety of colours (first photo) but with a bit of mixing you can expand your options quite a bit (second photo). You only have 30 minutes to work with the Sugru so try and plan your colour mixing out ahead of time so you still have plenty of time for your project.

A multi colour 8 mini-pack bundle of Sugru is $18 USD.
It contains:
2x Yellow
2x Red
2x Blue
1x Black
1x White

The larger blobs in the photo are an entire mini-pack and the dots on the board are about 1 inch spaced.

Step 1: Orange

The dark colours can be overpowering. With equal parts yellow and red you get an orange that is very close to the standard red (first photo). For a true orange you will need about 2 parts yellow to 2 parts red (second photo).

Step 2: Green

Again keep in mind that blue can be potent. Use 2 parts yellow to 1 part blue for the green in the photo.

Step 3: Purple

Mixing equal parts red and blue will give you a dark purple.

Step 4: Brown

Mixing all the colours in equal parts will give you brown.

Step 5: Lightening Colours

The purple created by mixing equal parts red and blue ended up being very dark.

If you are looking for a lighter purple you can use white as needed. The light purple in the photo is about 1 part of each red, blue, and white.

Step 6: Grey

As expected white + black = grey. Black is very potent so use it sparingly so that you don't end up adding your entire white mini-pack to get the grey you want. The grey in the photo is about 2-3 parts white to 1 part black.

Step 7: Darkening Colours

Black can be used to darken colours but, as explained with Grey, a little goes a long way. Start off with a tiny amount. The black also seems to take longer to work in to give you a smooth colour rather than just black lines throughout your original colour. Knead it thoroughly.

Sugru will build up on your fingers as you work with it. Especially with the dark colours and black be careful of contaminating your lighter colours. Have a few pairs of rubber gloves on hand or be prepared to give your hands a good scubbing between colours.