Is there anything such thing as a green smoothie that tastes nice?

[flumperoo]

Any ideas for a green, vegetable based smoothie that doesn't taste foul?
I made one with avocado, spinach, cucumber, coconut water and fresh mint thinking it would taste at least half decent - it didn't!
I've made lots of delicious fruit smoothies and have tried these with a bit of spinach added, which is also nice, but I'm looking for something less fruit based with more veg without needing a gazillion ingredients and that also tastes decent. Is this possible?

I use spinach or kale, celery, avocado, kiwi and apple with almond milk. Very green! I also put walnuts in it which works quite well.
Apparently lettuce in them tastes ok but makes you pee a lot!

Does it have to be Green? Because beetroot is delicious in juices, though I like things with avocado too as I think it makes taste like banana.

I use spinach, celery, cucumber, honeydew melon, apple, coconut oil, almonds and iced water

Thanks for the suggestions, I'll give them a try. I like the ida of apple as a sweetener but didn't imagine it would blend down very well without a super-blender rather than my bog-standard one. I also like the idea of beetroot. By green, I guess I meant veg based. Thank you.