If you have used two different cameras ie make and/or model then you have an almost impossible task trying to achieve colour balance between the two video streams and MEP will not be able to handle the adjustments required.
If both streams were recorded with 2 cameras of the same make and model, then you may achieve a close balance using the colour and colour correction under the Effects tab, Video effects. With the Colour option try setting the white balance in both streams and the Auto color
If you are using still images let me know and I will post a technique, using an image editing program, which works very well