for "true / false" part:

=IF(ISTEXT(REGEXEXTRACT(A1;"sites"));"True";"False")

for "more words crossreferenced with another sheet" part:

=IF(ISTEXT(FILTER({'sheet1'!A1:A3};{'sheet1'!A1:A3}=A1));"True";"False")

You can use REGEXMATCH:

=IF(REGEXMATCH(A1, "sites"), 1, 0)

To explain, REGEXMATCH returns true if and only if the argument is a substring of your string.

1. First, use the MATCH Function to lookup the word in the list. If it finds a match, it will return the relative position, which is a number. If it fails to find a match, it will return an error.
2. Next, we'll use the ISNUMBER Function to check for a number. It returns TRUE for a number and FALSE if not.
3. Finally, we use the IF Function to check if the result of the ISNUMBER is TRUE, which means there's a match. We return "Yes" for TRUE and "No" for FALSE.

Here's the final formula:

=IF(ISNUMBER(MATCH(B5,A:A,0)),"Yes","No")

For the specific case on the question it looks to me that the formula included already has the simpler formula

=IF(OR(A1="Cyan",A1="Magenta",A1="Yello",A1="Key"),"CMYK","Other")

as the alternatives are more complex in one or another way.

IFS and SWITCH are pretty new Google Sheets built-in functions. Side-note: their help articles are not translated yet to Spanish. If they were found to not be any less verbose, then the following examples of alternatives will not found any less verbose either.

• Using MATCH returns a number or an error and it requires that its second argument to be an array or a reference to a range. If it doesn't found the input value, it will return an error so it use for this case implies a way to catch the error.
• Using VLOOKUP also requires that its second argument to be an array or a reference to a range. Also if it doesn't found the input value, it will return an error so it use for this case implies a way to catch the error.
• The use of REGEXMATCH to be considered "simpler" implies that the formula writer feels comfortable writing regular expressions and that simpler doesn't mean shorter, as the resulting formula will be larger than the above formula.

If "foobar" is all in one column, I think a simple solution would be to create a filter, then click the dropdown to select foobar.

Check out the section titled "Filter your data" on this link https://support.google.com/docs/answer/3540681