Dutch website Inventor Wizard have created appearance libraries for Inventor containing all of the European RAL standard colours. There are 3 flavours on offer: generic, metallic highgloss, and metallic matte.
The site is in Dutch but can be automatically translated by Google. The colour names shown in the appearance browser are also in Dutch, but we have converted these to English if you prefer to understand exactly which colour you are choosing when you select a RAL code. The converted appearance library is available here (1.8mb zip)
Place the adsklib file with your Design Data, then add it to your project file's Appearance path if you wish to use it in it's entirety as a separate library.
If you would like to add some or all of the colours to an existing library, open it in your Appearance Browser then right click and Add To > your library on each colour you want to use.