5-H (not S-H) Haze Gray is the official WWII US Navy paint color, used in all its painting manuals, instructions, etc. of the time. It had a specific color, composition, and so forth, as would be expected.

Various brands of hobby paint makers all make different paint lines. Many are not aimed at model ships, specifically. They may be geared towards railroads, cars, armor, or aircraft, or might just put out a general range of colors that they feel will cover a wide range of topics.

They then also do not use consistent names for their colors. Things like "rust red," or "eggshell blue" are fanciful descriptive terms, but do not match anything official. The same generic color in one paint brand might be called something else by another brand. Sky blue, eggshell blue, light blue... Adding to this chaos is the fact that different brands often have different standards, such that--even when two brands are trying to produce the same official color--they might both end up slightly different from each other.

So... In this specific case, "light gull gray" is a common aircraft range paint color, and even then, it could be slightly different looking depending on if it was made by Vallejo, Polly Scale, or whomever.

Whoever told you to use it probably also gave you a specific brand, like..."I like Polly Scale light gull gray. I think it's a good match for 5-H."

There are a handful of paint brands that do produce specific paint lines for model ships, and in those lines, they will use the actual name of the color that the Navy used for it. For example, White Ensign Models Colourcoats paint line (one of the earliest/first brands to make lines specifically for ship modelers) will sell you a paint actually labeled 5-H Haze Gray, and it will have been matched by them to the official Navy color.

Otherwise, if you are buying your paints from a store shelf, and using one of the major brand lines, you probably will not find a paint in their range labeled specifically 5-H. They may well have the color you want, but it will be called something else (like, "light gull gray.")

This is what makes the subject of painting model ships very complicated. It is not straightforward. You will find as you get more into this hobby that there are websites with charts that will give an official color (like 5-H) then list all the possible matches for it in various different popular paint lines from different brands.

So... Your cammo book is accurate. The official US Navy color to use is 5-H Haze Gray with MS-22. However, finding a bottle of that color, labeled that way, will be challenging. If you prefer a certain brand, you were probably told that what the best match for the official color in that brand is their paint labeled "light gull gray." (And other brands might either call it something else, or possibly not even offer the right color at all.)

Hope this has helped.