The higher the values, the brighter the color will be, you can try to add a random value to a large number ( 200 in this case):
var randValue = Math.floor(Math.random()*56)+200;
Note: the maximum value of HEX is FF , which is equal to the decimal value of 255
You can then convert these RBG values โโto HEX using .toString(16) , but as far as I know, you can set colors using RBG values.
Here is the jsFiddle Demo
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