A jar of 70 candies has the following colors: 28 orange, 7 white, 14 brown, and 21 yellow.

The probability of randomly drawing an orange candy is $\dfrac{\text{\# of orange candies}}{\text{\# of total candies}} = \dfrac{28}{70} = \boxed{\dfrac{2}{5}}$.

To find the probability of randomly drawing an orange candy, we need to calculate the ratio of the number of orange candies to the total number of candies.

The number of orange candies is 28, and the total number of candies is 70.

So the probability of randomly drawing an orange candy is:

P(Orange) = Number of orange candies / Total number of candies = 28 / 70.

Simplifying this fraction, we get:

P(Orange) = 4 / 10 = 2 / 5.

Therefore, the probability of randomly drawing an orange candy is 2/5 or 0.4, which can also be expressed as 40%.