All children are diffeent - please don't worry yourself and compare them to others. My dd is 2.3 and knows her colours (even gold and silver) but she doesn't remember shapes very well. She knows circle & triangle but struggles wioth others. Kids will pick it up eventually so please try not to worry.
It's just when I hear that others are doing so much more, I wonder if it is because I don't spend enough time with them. They love colouring but I never get the paints out as it would be too messy with 2 of them.
They all learn different things at different times. They are still young. I wouldn't worry about it, although have to admit that I did start a thread once (some time last year I think) asking a simialr question - out of curiousity.
At my DS2's 2 year check, the health visitor said it was very unusual for a 2 year old to know even one colour consistently/accurately,and I guess she saw lots of 2 year olds! Both my boys 'got' colours around 20-22 months, but neither could pedal a bike/trike till 3.5 plus (in fact don't think DS2 can do it yet, at 3 yrs 6 months).
dd2 knows her colours, but i think that stems from having a sister a couple of years older than herself, as dd1 is always chatting to dd2 about colours. they colour in together. we also talk about colours a lot. the same with numbers (what colour is that car? how many steps are there? look at that bird and all it colours etc etc)
I was at a friend's house yesterday and she was obsessing about her ds 2y 3m not knowing his colours. She is asking him all of the time and trying to teach him. I have no idea what a normal age to know them is. My ds2 has known pretty much every colour since approx 22mths he had a book one day and kept asking me each colour and just seemed to know them after that, he is the same with shapes even remembered oval and octagon but always gets confused on circle. As I say I just it doesn't seem unusual for me that ds knows them but obviously my friend has nothing to worry about. They are all different and have their own talents I am sure they will learn in their own time.
The other day I pointed to a picture of an orange in a book and asked my dd what shape it was. She proudly proclaimed "YELLOW" So, we're clearly struggling with colours AND shapes. My dd is 27 months.
I figure she'll get it in her own time. No amount of working on it has helped so I guess she just doesn't get the concept yet. Just think of all the other things your toddler has learnt that he/she just got on their own int heir own time, without you having to work on it with them. I would not worry at all. Just keep talking about colours whenever it is appropriate.