What is the best way to store product size and color for an Ecommerce database?
You will need to implement exclusive subtypes to handle the attributes for each product type.  A (very) abbreviated example:
CREATE TABLE ProductType
(
  ProductTypeCd  CHAR(4)      NOT NULL /* Something human readable - SHOE, SHRT, BAG, BALL, etc */
 ,Name           VARCHAR(50)  NOT NULL
 ,CONSTRAINT PK_ProductType PRIMARY KEY (ProductTypeCd)
 ,CONSTRAINT AK_ProductType UNIQUE (Name)
)
;

CREATE TABLE Product
(
  ProductId      INT           NOT NULL /* If you have a code to track inventory/items, use that instead */
 ,ProductTypeCd  CHAR(4)       NOT NULL
 ,Name           VARCHAR(50)   NOT NULL
 ,Description    VARCHAR(200)  NOT NULL
 ,Price          DECIMAL(9,2)  NOT NULL
 ,CONSTRAINT FK_Product_Discriminated_By_ProductType FOREIGN KEY (ProductTypeCd) REFERENCES ProductType (ProductTypeCd)
 ,CONSTRAINT PK_Product PRIMARY KEY (ProductId)
 ,CONSTRAINT AK_Product UNIQUE (/* Whatever columns are necessary to prevent duplicates - if you are using a product code/inventory code for your PK this may be unnecessary */)
)
;

In this case ProductTypeCd works as a discriminator to define the subtype of Product, which we would then define like so:
CREATE TABLE ProductShoe
(
  ProductShoeId  INT NOT NULL
 ,GenderCd       CHAR(1)  NOT NULL /* M/W/U, should control through FK reference */
 ,ShoeSizeCd     CHAR(4)  NOT NULL /* 9/9D/9DD,12E, etc., should control through FK reference */
 ,ColorCd        CHAR(3)  NOT NULL /* Something human readable, RED, BLK, YEL, GRN, BLU, etc., again enforce through FK reference */
 ,CONSTRAINT FK_ProductShoe_Is_Product FOREIGN KEY (ProductShoeId) REFERENCES Product (ProductId)
 ,CONSTRAINT PK_ProductShoe PRIMARY KEY (ProductShoeId)
)
;

CREATE TABLE ProductShirt
(
  ProductShirtId   INT      NOT NULL
 ,GenderCd         CHAR(1)  NOT NULL /* Same treatment as for Shoe */
 ,ShirtTypeCd      CHAR(4)  NOT NULL /* TEE, POLO, etc. */
 ,ShitSizeCd       CHAR(4)  NOT NULL /* XS/S/M/L/XL/XXL/etc., again, use FK */
 ,ColorCd          CHAR(3)  NOT NULL /* Same treatment as for Shoe */
 ,CONSTRAINT FK_ProductShirt_Is_Product FOREIGN KEY (ProductShirtId) REFERENCES Product (ProductId)
 ,CONSTRAINT PK_ProductShirt PRIMARY KEY (ProductShirtId)
)
;

There is some care that must be taken to ensure the tables align with the proper ProductType.  Depending on the DB engine this would have to be handled via a trigger instead of a check constraint.  This SO answer handles it in depth: https://stackoverflow.com/a/4898314/13942986
From comments:

@Eniola so currently I am on the planning/design phase and I will be
using a relational sql database thinking of using SqlLite or Mysql

SQLite is not a relational database, MySQL barely so.  Between the two, use MySQL.