There are a ton of these cool logos around. Have a look at this selection at Vectortuts. I especially like the North Colour one. The beauty of nature in a curve and the visible spectrum. I tried to do something similar using a sine wave. I used the function plotter to plot the curve sine(x) using loonquawl’s post here at Inkscapeforum.com. The spectrum is a group of tiled clones of a slim, tall rectangle. the colour was shifted by column about 9% starting from red and the clones themselves were shifted 30% by column (why? I don’t know. Trial and error). I multiplied the curve and turned everything into a path. Then I did a difference with the curves and the bars. The bars have gradients (bottom to top) from opaque to transparent. I did the gradients by eye but I’m sure you could duplicate the curve, push it up and snap those gradient handles to it(?) or maybe not use the function plotter but use a grid with snapping to draw your curve then snap the handles to the grid(?).
Doing the research for this led me to this blog by John D. Cook. I never thought I’d say this but I WANT THAT PARAMETRIC CURVE.