try something like (untested but you should get the idea)
B4X:
sub pnl_Touch (Action As Int, X As Float, Y As Float)
Dim mPnl as Panel
mPnl = Sender
Select Action
Case pnl.ACTION_DOWN
pnl.color = colors.orange 'Highliightcolor
Case pnl.ACTION_UP
pnl.color = colors.black 'normal color
End Select
end sub