I can't remember where this came from - UT or other site.
I think you can modify to meet your needs.
I had a test form that I tried this on at one time.
Ken Paulson

local lnfstep,loLine
thisform.LockScreen = .t.
lnBandCount = iif(thisform.Height>255,200,thisform.Height)
lnfstep = ceiling(thisform.Height/lnBandcount)
* lnfstep = iif(lnfstep=1,2,lnfstep)
lnDeltaRGB = int(255/lnBandCount)
lnDeltaRGB = iif(lnDeltaRGB = 0,1,lnDeltaRGB)
for i = 0 to lnBandCount
loLine = [Line]+alltr(str(i))
loLine1=[thisform.]+loLine
if type(loline1) =[U]
thisform.Addobject(loLine,[Line])
&loLine1..Left =0
&loLine1..Height = 0
&loLine1..Zorder(1)
&loLine1..Visible = .t.
endif
&loLine1..BorderWidth = lnfstep
&loLine1..Top = &loLine1..BorderWidth*i
&loLine1..Width = thisform.width
&loLine1..Bordercolor = RGB(0, 250,(255-i*lnDeltaRGB))
endfor
thisform.LockScreen = .f.