I have always considered that "muddy" meant brown tones added to a colour. One can make brown by mixing yellow, red and blue.
Daylilies can have yellow pigments in their flowers - the carotenoid pigments. When these are in high concentrations they can be orange (there are also more orangey carotenoid pigments).
Daylilies can have reddish pigments in their flowers - the anthocyanin cyanidin pigments (reddish-purple).
Daylilies can have bluish pigments in their flowers - the anthocyanin delphinidin pigments (bluish-purple).
The carotenoid pigments are in the middle layers of the petals; the anthocyanin pigments are in the outer or very upper layer of the petals.
The carotenoid pigments are usually in little packets in the cells; the anthocyanin pigments are usually dissolved in watery liquid in the centre of cells.
There are also light yellow, cream pigments related to the anthocyanin pigments and located in the same petal layer and position in the cells. Call these precursors.
I think that if a petal has large amounts of carotenoid pigments and has anthocyanin pigments one gets some brown or mud. Since the anthocyanin pigments are in the uppermost layer of the petal sunlight or high temperatures may decrease their amounts during the day leaving the more yellow carotenoid pigments visible. Possibly why 'Matt' tends to be more muddy on some days and then become more yellow and less muddy during the day. Matt seems to show an overlay of muddy colour.
I think that no matter how much of the yellow precursors a petal has with anthocyanin pigments one does not get any brown or mud.
To get brown/muddy colours one has to have some anthocyanin pigment and these are always affected by temperature, sunlight, etc. (environmental factors). I think that the bluish-purple delphinidin pigments are more affected by environmental factors than the reddish-purple cyanidin pigments.
