住友商事株式会社 - Sumitomo Shoji Kabushiki Geisha, page-54

1️⃣ “Foundations” refers to the groundwork of the project and its financial stability, which is "rock solid." This is a metaphor often used to describe something as being strong and reliable.

2️⃣ "Sky above is blue" can have a double meaning. On one hand, it might simply mean that the weather is good (literally a clear blue sky). On the other hand, it can also mean that the future prospects of the project are bright and promising.

So, this phrase is a clever way of saying that the project has a strong foundation and a bright future, while also using a pun on the words "rock" (in "rock solid") and "blue" (in "blue sky").