If you look at the way the image data is written you'll understand why you got a blue square. Even though the array data type is 4 bytes (32 bits, U32) the data is actually 3 bytes (24 bits) for each pixel. The MSB is the red value, next is the green value, and the LSB is the blue value. Since you were using an array of U8 LabVIEW coerced all data to U8 which made most, if not all, pixels 255. Any pixel that had a red or green component ended up solid blue.