I'll add my voice in agreement with those who like 'Mary's Gold'; the flower form may be older, but the color is strong and grabs you.
For bright yellows, I am partial to 'Osterized'. There are other yellow daylilies that I like, but I always look forward to FFO on this one. (I feel the same way about 'Sears Tower', but it is a golden yellow polychrome (as opposed to the lemon yellow of 'Osterized'), and 'Osterized' is brighter.)
'Osterized'
Reds can be all over the map in terms of color: coral red, orange red, red, "candle" red (whatever that is), burgundy red... To this day, there are only two red daylily cultivars (ignoring seedlings) that I can recall which grabbed my attention solely by virtue of their color. In each case the daylily grabbed me and reeled me in from a distance; one, from across the garden (on a Regional tour) and the other, from the opposite side of a daylily nursery. These are, respectively, 'Hotter Than July' and 'Justin Brent'. (I have a seedling out of 'Justin Brent' which I also like very much for its bright red color. It needs a little work; I hope that I can keep the color!)
'Hotter Than July'
'Justin Brent' (not a great photo, sorry)
