I have a logo in white+blue. And I have a background of same blue color. If I simply put a logo over the background - logo's blue part merges with the background. How should I solve such a dilemma? P. S. I am not a designer
There are a number of different ways you could go about it solving this problem, each with their own pros and cons. The method you choose should reflect your consideration of these in the context of your use case. For example...
You could add a border around the logo. This creates a firm separation between the logo and background, but it messes with the integrity of the logo, and could be confused as being part of the logo.
You could add a drop shadow behind the logo. This separates the logo and background, more subtly than the border (which may or may not be desired). It also has the effect of adding another layer or plane to your overall image -- the logo is now 'floating above' the background (again, ask yourself if this is desirable or not).
You could add a containing element between the logo and background. For instance, a simple white (or what have you) box or card can contain the logo and set it apart from the background.
You could alter the saturation of the background. Either desaturate it to bring the logo forward, or oversaturate it to achieve the inverse. However, this solution is quickly strolling away from the parameters you specified.
This list is just a starting point, but it gives you an idea of the ways you can achieve what you want, and the consequences to consider in doing so.
Usually when logo brand guidelines are established companies create alternate versions of their logos for backgrounds with conflicting colors.
You might consider making an all white (or alternate/monotone color) version of your logo. Doing this to highly detailed logos can get tricky sometimes. If so, try outlines or removing unnecessary superfluous details entirely.