You need an image editor that can handle transparency, and save in a format that supports transparency (GIF, TIFF, PNG (not JPG!)). I know Photoshop could do it, but there are some free alternatives like GIMP. If the background you want to eliminate is simply a solid color, this online tool might work.
If you want to, PM me a link to the picture and I could try to Photoshop out the background.
From what I've read, I learned that each person with chromesthesia sees different colors for the same notes or chords, so whereas a song in the scale A major is only either turquoise or scarlet for me (depends on the instruments or tempo), A major may be a completely different color to another person with chromesthesia. Purple Haze, huh? Let's have a listen!
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Let's see... Purple Haze is sepia for me, and the intensity isn't very strong because there's some "background noise," like drumming, and not enough "musical notes." (Personally, songs that have the most intense color are usually solo pieces because they're uninterrupted by percussion.) The scale is in E-flat minor, from what I can tell anyway because it may not even be a minor or major scale but instead a Myxolydian or blues scale or something weird like that. It's really an interesting song! ... And I just found out through research that yes, the song is a combination of a Myxolydian and a blues scale.
I tried your test but actual numbers says my perception is lying to me. That band on the right is RGB(0,255,150) and so is blue and green in the spiral. Grab Paint.NET (for Windows), load the image and use the to check for yourself.
Even better, just download the image to your computer, go to LunaPic, upload the image and use their colour picker, you'll see it's the same value.