Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

What is the difference between a sun shower and a rainbow?

 A sun shower is a meteorological phenomenon in which rain falls while the sun is shining. It occurs when a layer of rain clouds passes over an area but the sun is still visible behind the clouds, casting a rainbow effect on the rain.

A rainbow, on the other hand, is a natural optical phenomenon that occurs when light is refracted, or bent, as it passes through water droplets in the air. When the refracted light hits the eye, it creates a spectrum of colors that appears as a circular arc in the sky. Rainbows can occur anytime there is water in the air, such as during a rainstorm or after a rain shower. They are typically seen in the sky when the sun is shining, and are most commonly seen when the sun is at a low angle in the sky, such as during sunrise or sunset.

So, while a sun shower and a rainbow may both involve rain and the sun, they are different phenomena. A sun shower is a type of rain that occurs while the sun is shining, while a rainbow is a colorful arc that appears in the sky due to the refraction of light through water droplets.