There is no general answer to this question.
A trademark prohibits sales using the mark or a mark that is confusingly similar to the mark.
The determination of whether two marks are confusingly similar is a question of fact that has to be resolved on a case by case basis, often with consumer surveys, evidence of actual incidents where the two were confused, or expert testimony.
Two marks that may superficially seem dissimilar could, in practice, actually result in large numbers of cases of actual confusion, while two marks that superficially seem quite similar may never confuse anyone.
The nature of the typical consumer matters. For example, in cases involving products marketed at children, one of the important empirical questions is whether the true decision maker in the choice between two products is the child or the parent. If the decision maker is the child, what is confusing is likely to be different than it is when the true decision maker is the parent.
As a practical matter, which could also be a defense if an infringement action is later brought, doing some focus groups or consumer surveys on the down low to determine if people actually get confused before launching your product may be prudent to avoid future risk.
It would also be useful to research the litigation history of the owners of marks that could potentially be claimed to be infringing. Some marks are vigorously guarded with regular litigation of potential infringers in even marginal cases, while other marks are placed in a file and never actually litigated even in the face of arguable infringement.
None of this is a guarantee, but it would help you to evaluate your risks.