Tru-Oil is very amber when its thick, and only slightly amber in thin coats.
In my opinion, Tru-Oil is a poor choice for instruments, especially necks... to me it has that "urethane" feel, and .. well.. not my thing at least.
You have two questions really - one is to color the neck, the other is to finish the neck in an oil type finish.
Tru-Oil is not going to penetrate the maple very well, so its going to build up a finish, and the color will be in the finish. As the finish wears, the color will wear off.
But, coloring hard maple directly is an iffy proposition at best.
My own choice would be pure tung oil, which you can get in an ambered (dark) form.
Pure Tung Oil provides a hard and tough surface finish that is absolutely waterproof; impervious to dust, alcohol, acetone, fruit and vegetable acids; and it doesn't darken with age like Linseed and other vegetable oils. All of these benefits come at a price - pure Tung Oil takes forever to dry, it doesn't penetrate the wood surface very well, and it is expensive when compared to other drying oils. Tung Oil is a "reactive" finish, commonly called a "drying" oil, in that it will dry and harden when exposed to air.
Everyone asks me about Tung Oil, but nobody wants to use it because Tung Oil is not a fast finish. It takes a lot of time. But, it is a simple and forgiving finish, and when done properly, its beauty is unmatched. Sometimes we try too hard to avoid the slow and simple things in our modern high-tech lives.
I have used the stuff for years and I can share what I have learned. Other oils are commonly used in finishes because they are less expensive. Linseed, Soybean, Walnut, Sunflower, Orange, and other fruit, nut and vegetable oils are oils that make suitable finishes for wood. Linseed and Soybean Oil are most often used in commercial finishes. Although neither are a natural "drying oil", the addition of metallic drying agents make them suitable for finishing. http://woodcentral.com.ldh0138.uslec.net/russ/finish6.shtml
PROPERTIES AND CHARACTERISTICS: A Pure Tung Oil all natural finish is water and alkali resistant offering a protective barrier. A Pure Tung Oil finish will not darken with age as other finishes will. It resists marring, penetrates well, remains elastic and unlikely to check. Tung oil builds quickly, consolidates the wood surface and builds a transparent matte finish. Pure Tung Oil finish will not mildew or bleed like linseed oil when dry which makes it an excellent candidate for outdoor finishes. It should be kept in an airtight container with minimum air space. Pure Tung Oil contains no thinners or driers and has a light nutty odor. A Pure Tung Oil finish mixed with Citrus Solvent is a all natural organic finish that is environmentally safe and food safe.
USE: The surface should be dusted to remove all loose particles. Alternatively, you can lightly sand the first coat before applying a second. Any filling, sealing or staining must be done before the oil is applied. The first coat should be a liberal one, and you can rub it over the wood with your hand, a soft rag. Allow this application to sit for 20 minutes so the oil can soak in, then remove any excess with clean soft rags. Check after about half an hour for any seeping, and rub this off as well. Let dry completely (24-48 hours) between coats. For woods with very open pores, allow an extra 24 hours drying time.
Tung oil can be applied pure or with Citrus Solvent added if a non-toxic finish is required. Thinners can accelerate the drying process and greatly improve the penetration by cutting the first coat of oil with Citrus Solvent, mineral spirits or turpentine by 50%. Remember by adding mineral spirits or turpentine, Pure Tung Oil becomes toxic with these substances mixed into it, although the finish produced is not toxic because the driers evaporate.
The number of coats of oil to be applied will be determined by the intended use of the piece. Two to four coats are enough for decorative work, paneling and moulding. Surfaces that receive moderate to heavy use or handling could need up to six coats for maximum protection, plus a light renewal coat a couple of times a year. Apply till the surface reaches the saturation point. This will be evident as the surface will not absorb more oil. Renewal and building coats are quickly applied with cheese cloth, a lint free cloth or old nylon stockings. This process will give you a surface that will stand up to vigorous use and spills: water will bead on the surface.
Pure Tung Oil is recommended for wood finishing of kitchen tables, chopping blocks, wood and concrete counter tops, wood floors, concrete floors, refinishing wood floors, outdoor decks, outdoor furniture, wood siding, log homes both interior and exterior and similar uses. Its non-toxic nature makes it particularly appropriate for children's toys and furniture. It gives good protection to wood paneling and molding.
Pure Tung Oil's matte finish will do nicely on certain pieces of furniture, but if a glossy finish is preferred you will need to buff and wax the finish, or use polymerized tung oil or a formulated tung oil based product.
We have found tung oil to be a valuable helper in the workshop. It adheres very well to metal, and a light coat rubbed onto tool steel is an effective rust inhibitor. Wooden handles will also benefit from the occasional coat.
I've used pure tung oil on cabinets, desktop accessories from organizers to lamps, gunstocks including very expensive figured english walnut and claro, and on one guitar neck... the results are hard, if impossible to screw up.
As the piece said, its only drawback is slow dry, a matter of a few days to a week, but... well well well worth the time. And it smells fantastic! Just thin it 50/50 with turpentine (or that citrus solvent... which BTW in a 90/10 mix with tung oil does great jobs on rosewood and ebony). Do the 50/50 on the first heavy coat.. .so as much soaks in as possible. After that, straight up. Nice finish that stays "silky" feeling after lots of use. You'll not got a big "shine" out of it, unless you wax it. Think - totally satin soft, like playing on powder.