In Processing the data type color is the same as an int and you can't " construct" an int trying to do so gives the error message you got. So you need to change line 8 to

1. class Cell extends Shape2 {
2.  
3.   // Inherits all instance variables from parent + adding one
4.   color c;
5.  
6.   Cell(float x_, float y_, float w_, float h_, int cr_, int cg_, int cb_, int ch_) {
7.     super(x_,y_,w_,h_); // Call the parent constructor
8.     c = color(cr_, cg_, cb_, ch_);          // Also deal with this new instance variable
9.   }

This is an alternative to the soultion given by tfguy44 both solve the problem and are equally valid  - so take your pick.

I think Quarks answered that here.

Well, you confused the compiler with your creative syntax... Beside, you had two opening parentheses, only one closing parenthesis, so the compiler expected who know what... Why not a triple dot there.

The simple answer is that the compiler got confused by the color( parameter, whether is was the missing closing paren of the color(  or the color( in the Cell(). The compiler has a faulty expectation as to what was intended and posts a cryptic, less than informative error message. This is often the case when closing syntax is missing and the compiler looks far beyond point of the error trying to resolve things.

As stated the compiler gets confused and attempts to provide the best possible error given its interpretation of the circumstance. When it can no longer find what it thought should be next, int this case ... it announces the error.

Some error messages can be confusing but in this case the triple dot does not mean ultra-bad error. The triple dot is used when a function can have a variable number of parameters, it is not used often but here is a class I created  that uses it.

1. import java.text.MessageFormat;
2. import java.util.Locale;
3. public class Message {
4.     public static String build(String pattern, Object ... arguments){
5.         return (pattern == null) ? "" : new MessageFormat(pattern, Locale.UK).format(arguments);
6.     }
7.    
8.     public static String println(String pattern, Object ... arguments){
9.         String s = build(pattern, arguments);
10.         System.out.println(s);
11.         return s;
12.     }
13. }

Both methods expect a string followed by one or more variables. For instance the statement has 4 parameters

Message.prinln("There are {0} {1} the fastest is {2} mph", 55, "circles",  78.9);

and will display
There are 55 circles the fastest is 78.9 mph

In your code you have
c(cr_, cg_, cb_, ch_);
where c is of type color (int) so it is complaining that it can't find a method with multiple parameters.