oops paint n. house paint sold at a discount because it is deemed of low quality or unsatisfactory color, has been returned by a previous customer, or was specially mixed but never sold. (source: Double-Tongued Dictionary)
oops paint n.— «I went to Home Depot and found a rack of oops paint. Mixed but never bought. I think I paid less than $2 for a quart. I was going to use black but only found a very dark purple.» —“Re: Painting back of tank...