Worrier28, I'm black and my back and stomach are MUCH darker than anywhere else on my body. My arms consist of a darker tone on the outside and a lighter tone on the inside. My chest is light compared to my neck. My neck is dark compared to my face. My forehead is darker than my chin. God, I'm beginning to sound like a complete freak now, aren't I???
I guess what I'm saying is I wouldn't worry too much about differences in skin tone. In darker coloured people, it is not unusual. You'd be hard-pressed to find ANY human being (dark or light) that has the same skin tone over their entire body.
And re: the HVs at babyclinics, I swear I sometimes want to bash their skulls in! I had one insist that my DS1(at 5wo) was jaundiced. I told her he wasn't - it was just a combination of his skin colour (DS1 is mixed race black/white) and the yellow poster hanging up on the wall casting a weird light on him. She was still insistent and called over her colleague to get her opinion. I eventually had to drag DS1 naked outside into the natural light to show them that he wasn't!! I also told the HVs that he had really bad reflux. They insisted that he was just spitting up normally. DS1 is now on medication for severe reflux, confirmed by my doctor
Scaremongering fools, the lot of them! Given that they couldn't even be bothered to answer any of the REAL pressing questions I had about DS1 (they simply treat it as a weighing clinic and nothing more, unless they want to stick their oar in), I haven't been back since.
Not saying that you shouldn't go to YOUR baby clinic but, sometimes, it's best to take what some of this supposed educated HVs say with a pinch of salt. And of course you should moisturise your DS's body - dry skin could further aggravate his eczema and any itchiness caused by it.