Can you please specify what the colours actually are?
RGB/CMYK/Pantone, whatever, but give levels, percentages or numbers.
Also, why do you trust a machine better than your eyes when it comes to colour harmonies?
The old-fashined way of getting colours to harmonize satisfactorily was to select hamonies and complementaries; so-and-so many of each.
But you must be more specific as to your needs. How many other colours do you want in all?
The colors being used are RGB colors #75959B and #6BB130. I am still working on developing my ability to select colors that work harmoniously together, that is why in the meantime, I am hoping to use the Illustrator Color Guide.
I am trying to create instructional handouts that use screenshots from Evernote, and Evernote uses green #6BB130 as the dominant color (see attached). I am trying to find a solid color that will work well with this green that I can use to create a banner at the top of each page (see second attached image) that will have a title on it and some other info. This solid color of the banner also has to work with #75959B because that is the color that will be used for the logo.
Try drawing a few rectangles using your two colours.
Take one of them and move one or two of the RGB sliders a little until you have another colour that you are happy with.
Then another and move the sliders in the other direction and so on
Try making one step blends between colours, keeping an eye open for colours you like.
Experiment with complementaries (Color panel, fly-out menu) and inverted colours.
There’s no rocket science behind this but it’s a good way to experiment; better than any automatic colour guide.