I wear my leather jacket all year round, I've worn it this week when it's been cool in the mornings and chucked it on over a t shirt whenever it's gotten a bit overcast/showery. I wouldn't wear it in full sunshine midday, but that's just for practical reasons not because I think it looks odd. They don't tend to be massively warm anyway.
Tights are trickier but it would have to be over 20 degrees for me to think "nah not today". Of course black opaques can look a bit odd in August but a sheerer pair wouldn't phase me. I'm not a big wearer of dresses/skirts generally though.