Need help understanding tweak palette "First & Last"

Could someone explain what First & Last do in the feature "tweak palette (red, green, blue, first, last)?" I'm having trouble understanding it. What especially confuses me is the range is from -63 to 63... what do these numbers represent? I'm assuming they somehow relate to the master palette, and thus only let the "tweak" effect a given colour range...? If so, this could be very helpful for what I'm doing.

In my game I was planning on doing hallucination sequences, similar to the effects eating magic mushrooms. After just recently learning how to use timers I decided that timers lend a perfect way to accomplish such a code. So I went ahead and made a code using "tweak palette (red, green, blue, first, last)." But I think the effect would be even more amazing if it only effected a certain colour range. Like the greens for instance.

If you want to see what the code looks like thus far I have posted a short video here:
https://www.youtube.com/watch?v=_gCUaCrW0eE&index=3&list=PL5FafLrq9rotB0E1nGNIUkehH6wejO_Rr

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⊕ P E R S O N A L M U S I C: https://open.spotify.com/album/6fEo3fCm5C3XhtFRflfANr
⍠ C O L L A B M U S I C: https://dustpuppets.bandcamp.com/releases

First and last refers to which parts of the palette you want to tweak. The range for those variables are 0 to 255.

For example, "tweak palette(63, 0, 0, 0, 255)" would redden the entire master palette (which is the same thing as if you left out the first and last variables entirely).

"tweak palette(63, 0, 0, 128, 255)" would only redden the colors on the bottom half of the master palette.

Thank you. That explains it perfectly. I mistakenly thought that the range for first and last was -63 to 63. Now it makes sense.

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⊕ P E R S O N A L M U S I C: https://open.spotify.com/album/6fEo3fCm5C3XhtFRflfANr
⍠ C O L L A B M U S I C: https://dustpuppets.bandcamp.com/releases