what do you mean easy?
surf green has no blue in it and is a lighter shade of green
sea foam green is darker with more blue in it (no yellow)
Let's first agree that yellow + blue make green. 
The 'smiley is green, both yellow and blue are neccesary to get there. There's also some red & black in that particular graphic.
Paint mixers, like printers have only 4 pure colors to start with: Yelo, magenta, cyan & black. These are yellow, red, blue & black (YMCK) with no additional colors added to them. These 4 colors are the foundation that make up all color swatchbooks for the color printing industry.
You can look at a fiesta red and admit that it is more orange(y) than candy apple. Why? There's less red and more yellow in fiesta red. The greater amount of yellow pushes the 'red' warmer. Candy Apple has a greater saturation of red, quite possibly the same amount of yellow, and black & cyan to add DENSITY, to deepen the color. Candy cola, is going to have a saturated red, but even less yellow than candy apple thus, cooling the red down along with percentages of black and cyan added to tone it down even more.
Daphne Blue appears to have no yellow, but a small percentage of magenta added to tone down the pure cyan qualities of blue. Start throwing yellow into that color and it will move towards a surf or a sea foam depending upon the densities of the blue, and magenta already in place.
For paint, unlike 4 color printing. Mixers can add hybrid pigments to enhance colors beyond the yelo, red, cyan, black limitations to get greater saturation.
The same rules of color still apply:
The more yellow added to blue makes the green warmer.
Less yellow, no matter the density of the blue will make it cooler.
If you want to get even more technical; there's probably a percentage of magenta added to sea foam to add density along with a few more percentage points of cyan. They're small percentages & the changes are sublte, but noticeable.
Surf Green is a much cooler color...meaning less yellow, and probably a bit less blue. It is that easy. Sea Foam is a warmer and yes, denser color. No accounting for aging. That depends on the instrument & its care from its owners over the years.
Perhaps I identify tones this way as a result of 20+ years doing color separation in the printing trades. I used to do scans for covers for
Car & Driver magazine along with pics for the articles inside, along with hundreds of other types of photographs, transparancies, paintings, etc. Red cars were the most difficult because paint mixers can (as stated above) enhance colors beyond the YMCK industry standards of printers. The reds some automakers use was not something reproducable with the YMCK structure, but we did the best we could.