Negative brightness values do not seem to work


```
A[decrease_red] <= pfunc:interp, loops:1;
A[decrease_red, 1] <= P[c:-100%](+0,+0,-:16), P[c:200%](+0,+0,-:16);
```

```
A[decrease_red] <= ;
A[decrease_red, 1] <= P[r:1](+0,+0,-:16);
```

I have witnessed different behaviors. Sometimes simply nothing happens, sometimes the whole animation system freezes permanently. (the basic keyboard functionality seems to be unaffected by this) 
