Of course all Octane color settings are set to linear (gamma 1.0, response linear) ... if not of course the color that you pick in any LW color picker can't match the color you get in Octane, because plugin can't correct the color of the LW color picker. LW color picker doesn't know anything about film response or any other tone mapping functions that Octane has.
In resume ... LW color picker is working in linear color space, if you are rendering using Octane tone mapping functions (a film response, for example), color doesn't match because LW color picker doesn't know what is a film response.
Perhaps Standalone perform a tone mapping of it's color picker, I don't know ... but for example if you pick a 0.2 gray in LW, you only are going to get a 0.2 gray color in Octane if all Octane color settings are set to Linear.
-Juanjo