tom wrote:
My brother and I jointly own a rental that has to be repainted.

1 15X15X9 room and 6X15X9 hall is light ivory. Another15X15X9 room is
appears to be a very light green. We have no need to change these
colors.

My brother proposes to get a can of light colored paint, an off white
or beige I think. I proposed electronically matching all the paints
where we have do not desire to change the color.

Which of us is right?

My experience and theory says that you save time with the closest
possible match since you can go faster without worrying as much about
coverage.

His experience says that you will get sufficient coverage with any
light paint.

If the colors are close in shade but differ in color, then poor coverage
will allow the old color to show through more. If they are both very
pale colors but contrast, one warm and one cool, then the base color
would be more likely to show. I'm with you - take a sample if you can
and match the color as closely as possible.