The Replace Color filter needs to be told first what color it will be replacing. So if click on the Color to Remove: color well, the color palette should come up. Then from there, you can use the little magnifying glass to pick out the color you want to replace.
Then you use a similar process for the Color to Replace: color.
If that’s not working, can you post your logo? Maybe there’s something different about it which is causing the filter to fail in some way.
Ah, you’re right! It’s a pipette, but the cursor becomes a magnifying glass after you click on it (at least in earlier OSs it did). Here’s what you want to click: