Hello 2Kids1Bike,
There are a couple of books that contain information relevant to your intended activities. I particularly like
https://www.amazon.com/dp/1580118674/
I paid the extra $10 or so to get the spiral-bound version, and I wish all books were available spiral bound. Another helpful book is
https://www.amazon.com/dp/1604697954/
" What if I like the tint of the indoor grown flower though? Is there a way to recreate that into a seed? "
I don't know of any unique way to "recreate that into a seed". But the indoor tint might already be genetic, so if you self-pollinate the bloom you might get at least some specimens that look like your indoor specimen. Even zinnia seeds straight from a commercial seed packet can show some variability. I don't know of any different genetic rules for indoor versus outdoor zinnias. There are obvious environmental differences, such as bees and butterflies outdoors but not indoors. And there are differences in lighting, which could be a photographic factor.
You are off to a good start. It is impressive that you are successful at growing zinnias from cuttings. Very few people know how to do that.
From the standpoint of your zinnia plants, the differences in your lighting are affecting you a whole lot more than them. Plants need some blue light and some red light and don't have a use for green light (so they reflect the green which makes them appear green). Some indoor growers use just red and blue, which mixes into a hideous purple. If you are using fluorescent lights, the bulbs are frequently labeled as "cool" or "warm" or sometimes just the color temperature. (3000K for very warm (reddish), 5000K for cool (bluish), etc)
I have been doing this zinnia breeding thing for nearly two decades, so my lights are obsolete fluorescent shoplights. Contemporary lighting technology uses solid-state Light Emitting Diodes (LEDs).
If your preference is white zinnias, I should give you my "take" on white. Zinnias have a wide range of colors, which are based on several organic dye pigments. But zinnias, like snow, don't have any white pigment. Zinnia white is produced the same as snow, by fine clear cells in a varied arrangement. So when you cross white zinnias with colored zinnias you can get hybrids with a combination of dye color and structural color, like these examples.
Like I said, you are off to a good start. Incidentally, when I was a kid growing up on the farm, it was 4 kids, 1 bike. But we also had a pony.
ZM (Not associated with any product or vendor mentioned or linked)