How do the magnetic doodle boards work?  The ones with the stylus that
has the magnetic tip and a slide bar the erases what has been done. 
How can some be blue and others are black?  Different type of magnets?

Hi butchme,

Thank you for your interesting question.  

How Stuff Works - How Magna Doodle Works by Craig C. Freudenrich, Ph.D. 
http://entertainment.howstuffworks.com/magna-doodle5.htm

You'll see a Table of Contents with a menu.  You can click on any of
the titles and be taken to that page, or else click on NEXT PAGE at
the bottom of each page.  Pages include:  Introduction to How a Magna
Doodle Works, Inside a Magna Doodle, The Heart of It All, Magnetic
Pen, Magnetic Eraser, The Case, In Action.

On this page:  The Heart of It All explains the colors...

*  The magnetic particles are dark, small and fine (about 10 microns)
- This allows them to be seen easily, to stack up and to be nearly
unaffected by gravity.
   - magnetic oxides - black magnetite, gamma-hematite, chromium oxide, ferrite 
   - magnetic alloys - iron, cobalt, nickel 

*  Dye is mixed in - This provides high contrast to the dark magnetic particles. 
   - white pigment - most effective (concentrations of 3 to 10
percent) and most commonly used
   - colored pigments - in some Magna Doodles 

******

You might also be interested in the Etch A Sketch.  
http://www.howstuffworks.com/question317.htm

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Best regards,
tlspiegel