The palette functions operate in 3 modes:
1) n colours - Pal(6) - returns 6 colours from the palette
2) data - Pal(c(-4000, -2000, 100)) - return colours for 3 elevations
3) palette - Pal(palette = TRUE) - return the full palette and breaks
The palette spans -8000 to 1000 metres, values outside that range clamp to
the end colours.