Poops after solids.

We've started introducing solids to our baby she's a couple of days shy of 6 months and was ready to start. I've just changed a poopy nappy and noticed weird black bits in it. She had some banana yesterday so not sure if that's what caused it but she had a couple of poops since then anyway? Should I be concerned or would it be the banana?

She also had baby strawbery yogurt 10 mins before this dirty nappy so I'm not sure if it's the yogurt because the yogurt was just plain coloured with no bits in it.