I might express my opinion that at first sounds like agreement, but is honest in the end.
"Well, my opinion/idea is more nuanced than that, while I agree that we need to find a way to make things more fun on the cover, I actually think that green stars would be more appropriate than pink dots" Or even, "I agree that we need to find a way to make things more fun on the cover, but why don't we finalize the design off-line?" - this acknowledges an idea which might be valid (cover needs to be more fun), but takes the disagreement about details out from the lime-light.
Or "Tracking widget1 is a good idea, and for the same reasons, I also think we should track the other widgets. There is no additional time or cost to do so, and we could use the data in x,y and z useful ways."
"Yes, I love the clouds today" (if it doesn't matter, it softens the other disagreements)
If there's absolutely NOTHING about what supervisor just said that can be agreed with, even on a secondary level, then "There must have been a miscommunication between us, perhaps we should discuss it further and present that at the next meeting instead" This is neutral (no finger pointing about who miscommunicated, and also takes the disagreement out from in front of an audience).