This enchanting trifle

…There are three angles to every triangle you may remember; so there are three angles from which to consider this enchanting trifle of a triangular hat…

… Just to remind you that the striped hat can be made from oddments of wool in any number or combination of colours, so long as your bits and pieces are of the same ply and amount to about 1½ oz. in all.
That, for more formal wear, the same hat is very smart in one colour. Use a 4-ply wool, or bouclé yarn to match the LITTLE BLACK FROCK, or angora or any other fancy yarn. Be careful to obtain the correct tension if you use a fancy yarn, by working a sample first. If necessary, you can use needles of a different size. Remember that a firm fabric is essential, so that to obtain the stated tension, a thick yarn or a fine yarn used double, knitted on fine needles will be more effective than a fine yarn knitted on larger needles.
That if you  like both the striped and the one-colour idea, the same hat looks quite different if you wear it back to front!