Why is there an error in GmodLua?

Question

Lua

Addon - pLogs
Here is the error itself (it comes out when opening the logs, after I changed them to a dark theme):

[ERROR] addons/plogs/lua/plogs/lib/pdraw.lua:30: bad argument #3 to 'surface_SetDrawColor' (number expected, got no value)
1. surface_SetDrawColor - [C]:-1
2. Box - addons /plogs/lua/plogs/lib/pdraw.lua:30
3. SkinHook - addons/plogs/lua/plogs/vgui/skin.lua:185
4. unknown - addons/plogs/lua/plogs/vgui/tablist.lua :60

I just didn’t understand what was wrong there ((

PySy: These are the very lines:

30
surface_SetDrawColor(col)

185 60
plogs.draw.Box(1, 1, 3, h - 2, SKIN.ProgressBar)

derma.SkinHook('Paint', 'TabListButton', button, w, h)