Like on all the other areas of the car be consistent with the interior styling. If your car has a racy look then a bright colourful interior with 10 Tv screens may not be the best choice. For a racy look the interior should consist of Custom mounted gauges, racing seats, roll cage and lots of lightweight materials made out of carbon fibre and aluminium. For an exotic/wild style car you should include custom materials like vinyl or leather to re wrap the car's interior. Make sure the whole interior is covered from the roof liner to the carpet as points can be deducted for incomplete interiors.
Choosing the right colour
For choosing the right colours for the interior the decision should be based on the colour of the car. You should try to match it as closely as possible to the colour of the exterior of the car for example if your car is black then a black interior. On the other hand you can go for a contrast like a red car with a yellow interior. All the parts like the steering wheel, gear knob, handbrake and pedals should match the interior colour.
Another good way of deciding on a colour is to match it to the rims. If you have a silver coloured car with black rims, then having a black interior would make a nice contrast. Having too many different colours on the car makes it look messy and you will loose points at a car show.
Customizing the interior
In order to gain maximum points at a car show the interior needs to be customized as just re wrapping the car's interior in a different colour just won't do anymore. For example you can have Tv screens built into the centre console, gauges is unusual places, you've probably heard of some car's that have goldfish bowls and even a whole aquarium built into the centre console. Obviously you wouldn't have these extreme customisations if you are going for the racy or clean look.
Well that's it for the car's interior, most people know what their doing when it comes to this area on the car. Stay tuned for the next part in the building a show car series which will be about the car's audio and entertainment system.