For an in-camera result, the safest approach is to use your camera’s more saturated color mode rather than relying only on white balance. Try a Picture Style/Control or Scene mode such as vivid, vibrant, or sunny/beach if your camera has one. That boosts color overall and usually gives a punchier postcard look without making the whole image look unnaturally blue.

If you deliberately want a cooler, bluer rendering, you can set white balance lower/warmer than daylight, such as tungsten or around 3000K. That will shift the image toward blue—but it can also tint the whites blue, so it’s not ideal if you want white walls to stay neutral.

For the most control, do it in post-processing: increase vibrance/saturation selectively for blue areas rather than shifting the whole image. That lets you make sky, sea, and blue paint pop while preserving cleaner whites.

So: use vivid/vibrant color settings in-camera for a good starting point, but for strong blue emphasis with white whites, selective editing after capture is the better method.