For the tics:
set cbtics format "%1.1f"
The maxcolor
option of set palette
allows you to define how many colours are used.
zmax=1 zmin=0.3 zstep=0.1 set cbrange [zmin:zmax] set cbtics zstep set palette maxcolors (zmax-zmin)/zstep*2 splot [0:1][0:1] zmin+x*(zmax-zmin)