Most of my friends were surprised I was able to find science activities that could tie in with a Martin Luther King theme. After much research I found two listed below:  


1. Color mixing
Decorate an old sheet by spraying different colors (food coloring and water) from a spray-bottle all over it.
By mixing primary colors (red, blue, yellow) you find secondary colors (orange, green, brown, etc) 
Have the children watch the colors mix and talked about how people are different, just like the colors, but how they can live/work/share together (just like MLK believed). Then after the sheet dried I cut it into squares and let everyone take a piece home.
2. We’re All the Same on the Inside

This is a simple look at how we can look different on the outside, yet be the same on the inside. We use this activity around Martin Luther King day after a discussion about prejudice.
one or more brown eggs
one or more white eggs
a bowl

Plan: Following a discussion with the children about how people are alike (we all have two eyes, we all have hair) and how we differ (blue eyes vs. brown eyes-long hair vs. short) show them a brown egg and a white egg.

Discuss the similarities and differences in the eggs. (They are oval, they are different colors.)

Break each egg into the bowl and dispose of shell. (Hint: this is best done above their eye level because if they see which yolk came from which egg, they will be able to make a distinction). Can they tell which is which? No–because just like people,even though we may LOOK different on the outside, we’re all the same on the inside!