But your circles are covering halftone areas and therefore don't represent pure colours. If the right hand one is moved up or down to cover the green square then it would also encompass the brown overstripes too. Here are high-res extracts of the blue and green sections.
Blue square with light blue/green overstripes.
Green square with brown overstripes. There are a number of ways of getting brown with natural dyes. Traditionally a shade like that shown would probably have been obtained from a dyestuff like cochineal or madder (neither of which only give red) which would have been saddened, or one of several tannin sources. Slightly later Wilsons used imported the tropical hardwood known as 'Rid-wood' in conjunction with Shoemack and coppras to sadden the colour.
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