Yep, HOC is House of Colour. Threads about it can get quite heated - some people think it's great and others that it's a huge waste of money and it'll turn you into a frumpy Hyacinth Bucket. I've had my colours done (I'm a Winter - cool bright, clear colours).
I'm not sure - there are various online guides that you could try. If you're spring you'll suit bright warm colours. So warm orange reds like geranium rather than the blue reds. If you look better in gold then you're probably warm. You can look at the Kettlewell site as they group colours into seasons. They allow much more crossover than HOC though & most colours are put in more than one season on the Kettlewell site.
The consultation is lots of fun so if you can afford it (£110 I think) then I think it's money well spent. You get a wallet with swatches and they tell you your best colours. You have to go with no make up and they cover your hair then drape you with lots of different coloured scarves.
I found I was already drawn to the "right" blues and pinks, but it has made me more confident about trying other colours. I now know I'm absolutely right to avoid neutral beiges and oatmeals etc that look so fabulous and sophisticated on my mum but make me look tired and yellow (my mum's a spring).
Had this done a long time ago, and I'm Spring. Got a colour swatch to take shopping with me, which in theory is great, in practise you often don't get the colour choice when you're actually buying clothes, so a bit academic, unless other people spend much longer selecting clothes than me. Maybe I don't have the patient to seek them out!