To find the expected value, take the sum of the products of the value of an outcome and the probability of that outcome. Intuitively, this is a weighted average of the outcomes. If you were to roll this dice some large amount of times, add 1 or 2 to the sum depending on whether it landed on red or blue, and then take the average, you should _expect_ an answer close to the expected value.
In this case, "red" has a value of $1$ and "blue" has a value of $2$. Each has probability of $\frac{1}{2}$, so this gives
$$\text{Expected value }= \frac{1}{2} (1) + \frac{1}{2} (2) = \frac{3}{2}.$$