Furthermore, he undoubtedly fell into the error common to "specialists," or persons working for long periods of time on one subject--the error of over-enthusiasm in his subject.

He had discovered so many remarkable qualities in the air that it is not surprising to find that he attributed to it many more that he could not demonstrate.
Boyle's work upon colors, although probably of less importance than his experiments and deductions upon air, show that he was in the van as far as the science of his day was concerned.

As he points out, the schools of his time generally taught that "color is a penetrating quality, reaching to the innermost part of the substance," and, as an example of this, sealing-wax was cited, which could be broken into minute bits, each particle retaining the same color as its fellows or the original mass.

To refute this theory, and to show instances to the contrary, Boyle, among other things, shows that various colors--blue, red, yellow--may be produced upon tempered steel, and yet the metal within "a hair's-breadth of its surface" have none of these colors.

Therefore, he was led to believe that color, in opaque bodies at least, is superficial.
"But before we descend to a more particular consideration of our subject," he says, "'tis proper to observe that colors may be regarded either as a quality residing in bodies to modify light after a particular manner, or else as light itself so modified as to strike upon the organs of sight, and cause the sensation we call color; and that this latter is the more proper acceptation of the word color will appear hereafter.