Which colours can you see in the photographs?
2. The cat is black.
3. The tomatoes are red.
If you are going to write it with numbers, write them as above, but that way they are sentences and each sentence must start with a capital letter and it would normally end with a full stop. If you write it as one sentence it is probably better.
e.g. The colours in the photo's are orange, black and red.
I hope that helps.