[plt-scheme] Turtle Graphics

Hi,
I'm trying to do something with the turtle graphics
and I'm having some problems.

let's say :

(turn 43)
(tprompt (draw 100))
(erase 100)

The turtle will not exactly erase the last line. (leaves some pixels)

I would also like to use colors and make the turtle disappear 
during the painting. I couldn't find documentation on how to use
colors with the turtle graphics nor on how to make 
the turtle disappear.
Can I do these things with DrScheme?

Thanks in advance.

Petros Pissias