Can a blood orange be half bloody?
While many pictures show them deep red (perhaps for the dramatic effect?), even orange flesh wih only some red tinge is normal. 

Even the wikipedia link you gave in the question states:


  The Moro is a "deep blood orange" meaning that the flesh ranges from orange-veined with ruby coloration, to vermilion, to vivid crimson, to nearly black.


The color of oranges is affected by temperature: Only if there is a certain temperature difference (cool nights vs warm days) the oranges develop the deeper hues. For blood oranges the crimson flesh and reddish tinges in the skin, "normal" oranges get their typical orange skin instead of greenish or yellow. 

Fun fact: Even greenish oranges may be ripe, but just didn't get the cool nights. For the sake of the consumers who percieve orange = ripe, green = unripe, the skin of oranges and other citrus fruit can be "de-greened" by the "ripening gas" Ethylene (if permitted).

Below a range of color variations from mostly orange to deep red: