Visual changes
Reshade is a programm that allows you to add post-processing effects in video games. You cannot get VAC banned for this, I've been using it for 3 years now. This Reshade present changes the dull and washed out visuals of TF2 and makes them more vibrant and Cartoony looking. This also works in Casual.
Instructions:
Here is a good video that shows you how to download Reshade.
TF2: How to install ReShade made by Fracklo
You only need to download Standard- and SweetFX Effects.After downloading Reshade put the ini file in your bin folder in steam\steamapps\common\Team Fortress 2\bin and enable it through Reshade.
IMPORTANT NOTE:
Since the release of the 64-bit update you need to choose tf_win64.exe AND NOT tf.exe when you're using Reshade.