I did a quick search on this website and came up with this post from Ray Ivers.
The post subject was "74 MT250 My first project"
Here's what I got from the Honda parts info at Babbitt's:
TANK ASSY., FUEL *NH42M / R18* (CUSTOM SILVER METALLIC AND DAYTONA ORANGE) (Honda Motorcycle Code 0348789)
COVER, L. SIDE *NH42MC* (CUSTOM SILVER) (Honda Motorcycle Code 0350033)
FENDER, FR. *NH42MC* (CUSTOM SILVER) (Honda Motorcycle Code 0321737) - rear fender same
It appears the tank silver is metallic, while the rest of the bike is not.
Here's a couple of paint links - the audio on the first link is well worth listening to:
http://www.cyclecolor.com
http://www.twowheelparts.nl/en/paint
If you want to paint your bike just like it was originally done, be prepared to spend some money. The complete NH42M Custom Silver Metallic paint kit I got last year (base flex coat/color/clear coat, enough to do maybe 3 fenders) cost over $200.
Ray