The motherboard will be the final determiner. But usually you will want to use MATCHING* pairs of memory in like colored slots for best results. Some boards will not allow dual channel memory mode if the pairs are not identical. Test your system by trying both matching sticks in the same color slots first. If all is good, add the other single stick in one of the other color slots. Finally add the odd size stick in the final slot. You will know soon enough if it will work.
*That's why dual channel memory is sold in matching pairs.