In cases like this I prefer not to use one of the 2 colors already in the quilt because then the blocks seem to "bleed" into the border to me. I use a totally different color, something complimentary, to "stop" the action of the blocks....maybe a 2" wide narrow border, then one or more, pieced or not, of one of the block colors.
In you case, you've used 2 of the three primary colors (yellow[tan], blue, and red). So, I'd use something in the red family....rust/burgundy/deep orange/true red/etc. for that narrow first border. I think you'll be surprised how it would enliven your quilt.
Jan in VA