Degrees Lovibond is the unit used to measure the potential color affect of a given malt or adjunct. It corresponds to the color of the finished beer given in SRM (Standard Reference Method) units. For example, 1 pound of a 10 °L malt can be expected to given 1 gallon of water a 10 SRM hue.
While SRM is strictly speaking an empirical measurement unit, it is possible to predict the color of a beer ahead of time. To calculate the expected SRM of a beer, you take the sum of the malt color for each addition times the weight in pounds, and divide that sum by the volume in gallons. For example, if your golden wheat has a color of 2 °L (which is about typical for a wheat malt), and the carapils is 1.5 °L (again, about typical for that malt) then the SRM of your beer would be:
((2°L * 5lb) + (1.5°L * 0.3lb)) / 2.5 gal
(10 + 0.45) / 2.5
10.45 / 2.5
4.18 SRM
This is a rather light-colored beer, a little darker than, say, Budweiser, much lighter than what you describe. However, you have to recall that a) you are looking at it through the whole 2.5 gallons of it, and b) it is still fermenting, which means a lot of yeast is still in suspension in it. Once it clears, and you have a chance to look at it through a narrower glass, it should come out quite pale.
Most brewing software will automatically estimate the SRM of the beer for you.