How to solve the problem that the project module turns grey in Maven

wrong project, built to remove reconstruction, suddenly have been project identification, always prompt project can’t find, then see the maven inside of bar on the right, according to project is gray, the diagram below:

for this reason, find relevant solution and steps are as follows:
1 file – setting

2 maven – ignored files, the following figure

save after 3 o ‘clock, gray disappears inside maven:

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