I would like to begin contributing on Kotlin itself, but IntelliJ highlights every single line of the Kotlin project's Kotlin files with red errors. I have commented on the issue in the tracker (http://youtrack.jetbrains.com/issue/KT-1177) but am wondering how the IntelliJ team is working developing Kotlin.
The curent answer is don't open the project in IDEA with the Kotlin plugin installed.
If you are going to be fixing the plugin, it's no use for you to have it installed.
If you are going to contribute to the libraries, you don't need to compile the compiler sources.