Can I use food-coloring drops in my pancake batter to make "red & green" pancakes for Xmas am. ?

You could place a Santa cookie mold in the pan/griddle, pour in the red mix. Pour regular or the green mix around it on the outside, let the pancake set a bit, the gently lift the mold out.
Use other cookie molds like a tree or star or ...

Don't put both red and green coloring in the same bowl of batter!

Recently, I have been making the pancake batter in the blender, and throwing in a (big) handful of spinach for nutritional value. it blends in completely (in a Vitamix), and doesn't change the taste of the pancakes, and they're certainly green!

Yes, you can!