it would help if you posted a pic of your room showing the new paint. Choosing a paint colour has to be in context with the whole room, the flooring, natural light and furniture. I love stiffkey blue and have used it before but not combined with green. I think a lighter pink like setting plaster might go better with your card room green

Could you share a picture of the actual room?

I agree, a picture is needed to see how the colours look in your room, the sofa colour, floor colour etc

It would also be good to see the room size against the bookcase so there’s a balance of colour

I love your cushion! another option may be to paint just the inside of the bookcase although given a typical dado height most of the room sounds quite light? Maybe just using the red as an accent colour for accessories would work as painting the whole bookcase is likely just to draw your eye there but it depends what you want as the focal point

Neither blue or red, as it's a large surface. Pick a green inbetween the ones you got. Or a natural, greige, chocolate brown, your pick. Or that exact same card room green on the outside and an accent color like that red you got on the back wall of the bookcase (like minnies example).