I was able to guess the first two, they both look good. The rainbow, I imagined to be a bit more vibrant and ornate.
The rainbow was when I started, but it was so bright that it looked like an 8 year old's drawing... I always pictured the rainbow shell items as being less actually "Rainbowy" and more like a multicolored irridescent type thing... like an abalone shell is. Or I guess kind of like motor oil mixed with water, if you know what that looks like...
The red katana in my mind was always more of a red-orange color, and not really colored, but it relfected that color.
The Masamune is fairly similar to the artwork though... are there any swords you all would be interested in seeing my take on?