Here is a video demonstrating a method for manipulating paint spawns:

Summary of the technique:

1. Unlock 4/5 messages needed to unlock paint (see http://www.speedrun.com/talos_principle/thread/m8hra )
2. Enter a world with predictable paint (A5-7, B4-8, C1-8). For an explanation of paint prediction, see http://www.speedrun.com/talos_principle/thread/cd2w3
3. Look at a QR code (or use another trigger such as hitting an OoB reset) to get message 5.
4. Without hitting a checkpoint (such as entering a purple gate, entering a world portal, or collecting a sigil) check if paint is in the desired location.
5. If paint is not where desired, reset and return to step 3.
6. Once paint is in the desired position, hit a checkpoint to save that spawn configuration for the rest of the run.

Explanation: As soon at the 5th message is unlocked, the game generates a random number that determines where paint will spawn. Normally, this number is saved by the game and will remain constant for the rest of the run. However, this number is only saved after a checkpoint is reached. Resetting the game before reaching a checkpoint also resets the random number, allowing you to generate a new number and thus a new spawn.

A question for the community:

Should the use of QR codes placed by previous runs or by steam friends be allowed during a speedrun?

Using such QR codes would make the above technique much more useful as we could place QR codes right where we need them. The only issue I see is that using such QR codes requires some initial preparation, meaning that the run would no longer be possible with a "clean slate" game (i.e. offline, fresh install version of Talos).