Can dogs be colour blind?

OK so first of all, I know dogs can only see in dichromatic vision and therefore see the world in fewer colours than humans do.

However, I keep reading that blue is the best colour for dogs toys as it stands out best for them, and people recommending blue balls to throw on grass etc.

But my dog seems to really struggle with this! She can pick out a tennis ball on grass no problem, but she has a number of blue balls that she regularly loses and just cannot seem to find. I’ve watched her, many times, walk right over the top of them whilst she’s actively looking for them, and she just doesn’t seem to be able to spot them at all.

She’s a Labrador so loves playing fetch. I’m just wondering if dogs can be colour blind, so that the usual colours they see aren’t quite the same as other dogs?

I’m really struggling to find any information online because any time you search for dogs and colour blindness, all the answers are about dichromatic vision and seeing a reduced colour spectrum compared to humans.

I’m more curious than anything, but I’d also love to know if this is possible and if so, which colour toys will be best for her!

Many thanks.