Sexing Chicks

Is this impossible??

I have tried on several occasions to upload some pics of my week old chicks but I seem to be doing it wrong 

Two have the most perfect eyeliner like this...<o o> .....either side of their eyes. They also have a thick darker line down their heads and down their back. The other two are orange fluffy chicks and one is just a mixture of red and brown (quite cute actually). They have all got, what looks like, an orange spot on the back on their legs half way up..now when I saw this I thought oh no they are all COCKS!! thinking that this is where their spures (sp?) start growing??? Could do with some knowledge about this please 

we think that they are a mix of welsummer and black rocks with maybe a rhode island red!

so the spot on the back of the legs is nothing ??

thanks debbie