Rule 5a. reads, "...colored panel on the wing that is at least the length of the wing chord and at least between 2 wing ribs." Also, see the official Science Olympiad website FAQ responses below to questions related to this rule and rule 3g. I wrote these two question to the SO FAQ in order to get clarification on the concept of "non-transparent", etc. For the 5a. bonus the area bounded by the leading and trailing edge of the wing and two of the wing ribs (including, in my unofficial interpretation, covering the wing ribs and the leading and trailing edges themselves) must be covered in a colored material. As you can see in the FAQ responses below, coloring by dying, painting, coloring with a marker, etc. are allowed methods of achieving a "colored panel".
I have further questions submitted to the SO FAQ to get additional clarification so that event supervisors will hopefully not feel that difficult judgement calls are required regarding the quality of spray painting or marker application.
Pactra model car spray paint works well for coloring clear plastic and, if applied in a few light "dusting" coats, does not add significant weight.
AMA since 1972 (off and on)
Below copied from the official Science Olympiad FAQ webpage. However, of course, all official review of the FAQ should be done directly from the SO website.
(section: 3 / paragraph: g / line: 1)
2014-10-26 20:05 Please clarify "non-transparent" as even Esaki tissue is transparent enough to read through: Is Dying, spray painting, or coloring with a marker over clear plastic covering material allowed?
Yes, for the Science Olympiad National Competition, the techniques and materials as described but not limited to: dying, spray painting, coloring with a marker over clear plastic, are each acceptable and will be allowed as a covering so that aircraft may be identified at its maximum altitude.
(section: 5 / paragraph: a / line: 1)
2014-10-26 19:48 In the case of a tip-dihedral model, would a colored wing tip (which is non-horizontal) meet the requirements of both rule 5.a and 3.g.?