Concatenate a Checklist

I'm trying to create a two column checklist (column A for the "x" to be places if applicable, and column B for the list of items) and have only the checked items appear in a list later on.

Column B would list options (red, blue, green) and then column A would be used as a check list. Then in cell C10 I'd like to concatenate the Column B values for only items that have an "x" in column A.

So, if B1 is red and B2 is blue and B3 is green, and then there is an "x" in cells B1 and B3, I want the result in C10 to be "red green"

any ideas?

post sample file

Checklist Example.xlsx

Here is an example where I would want to put the formula in cells C6, C15 and C24