The first thing you should do is rub some used motor oil into that new pad to make it look somewhat more like the rest of the gun. Secondly, the checkering isn't so much dirty as it is worn. Unless you go for a total restoration, anything you do to the wood or metal to "improve" the look is going to stand out. Be careful.
JR

Be strong, be of good courage.
God bless America, long live the Republic.